*Most of the definitions are taken from Wikipedia, the free encyclopedia.

Music Music is a form of art. Music is also a form of entertainment that puts sounds together in a way that people like or find interesting. Most music includes people singing with their voices or playing musical instruments, such as the piano, guitar, or drums.
Musical Instruments Musical instruments are things used to make music. Anything that somehow produces sound can be considered a musical instrument, but the term generally means items that are specifically for making music.
Musical composition Musical composition can refer to an original piece of music, either a song or an instrumental music piece, the structure of a musical piece, or the process of creating or writing a new song or piece of music.
Rhythm Rhythm, in music, the placement of sounds in time. In its most general sense rhythm is an ordered alternation of contrasting elements.
Note A note is a small bit of sound, similar to a syllable in speaking a language. For example: in the first two lines of the song "Twinkle, twinkle little star, how I wonder what you are" there are 14 notes: one for each syllable. Confusingly, the word "note" can also mean the pitch of a note (how high or low it is). For example: the whole of the song "Twinkle, twinkle, little star" can be played using six different notes: C, D, E, F, G and A.The word "note" can also mean the written symbol of the note. Nearly all music is made up of notes. (Music without notes might be sound effects.) In Music Blocks, we use the note value block to designate the duration of a note. And we place pitch blocks inside the note value block to designate the pitch(es) of a note.
Pitch The pitch of a note is what a listener hears as means how high or low a note is. The pitch of a note can be measured in a unit called Hertz (Hz). A note that is vibrating at 256 Hz will be caused by sound waves that vibrate at 256 times a second. This will be Middle C on the piano. Music Blocks has many ways to specify the pitch of a note, including Hz, note name, solfege, pitch number, etc. Not all musical instruments give notes of a particular pitch. Many percussion instruments like drums, triangles and cymbals are instruments used for rhythms. They do not play tunes because they have no definite pitch (although often a definite pitch can just be heard when listening carefully.)
Melody A melody, tune, voice, or line, is a linear succession of musical tones that the listener perceives as a single entity. In its most literal sense, a melody is a combination of pitch and rhythm, while more figuratively, the term can include successions of other musical elements such as tonal color.
Melodic Pattern/ Melodic Sequence In music, a melodic pattern (or sequence) is a repetitive pattern or figure that can be used with any scale. It is used primarily for use in solos because, when practiced enough, it can be extremely useful when improvising. "Sequence" refers to the repetition of a part at a higher or lower pitch.
Musical Notation Music notation or musical notation is a way of writing down music so that anyone can play it. Many systems have been used in the past to write music. Today most musicians in the Western world write musical notes on a stave: five parallel lines with four spaces in between them. However, there are many others, some of which are in use today in different cultures. (In some sense, your Music Blocks program is just another form of musical notation; you can generate Western musical notation from Music Blocks using the save to Lilypond or ABC functions.)
Scale In music theory, a scale is any set of musical notes ordered by fundamental frequency or pitch. A scale ordered by increasing pitch is an ascending scale, and a scale ordered by decreasing pitch is a descending scale. (An example of ascending and descending scales in Music Blocks can be seen here).
Key In music theory, the key of a piece is a group of pitches, or scale upon which a music composition is created in classical, Western art, and Western pop music. The group features a tonic note and its corresponding chords, also called a tonic or tonic chord, providing a subjective sense of arrival and rest and also has a unique relationship to the other pitches of the same group, their corresponding chords, and pitches and chords outside the group. Notes and chords other than the tonic in a piece create varying degrees of tension, resolved when the tonic note or chord returns. The key may be in the major or minor mode, although major is assumed in a phrase like "this piece is in C". Popular songs are usually in a key, and so is classical music during the common practice period, around 1650–1900. Longer pieces in the classical repertoire may have sections in contrasting keys.
Chords A chord, in music, is any harmonic set of pitches consisting of two or more (usually three) notes (also called "pitches") that are heard as if sounding simultaneously. Chords and sequences of chords are frequently used in modern West African and Oceanic music,Western classical music, and Western popular music; yet, they are absent from the music of many other parts of the world. In tonal Western classical music (music with a tonic key or "home key"), the most frequently encountered chords are triads, so called because they consist of three distinct notes: the root note, and Intervals of a third and a fifth above the root note. Other chords with more than three notes include added tone chords, extended chords and tone clusters, which are used in contemporary classical music, jazz and other genres.
Interval In music theory, an interval is the difference between two pitches. An interval may be described as horizontal, linear, or melodic if it refers to successively sounding tones, such as two adjacent pitches in a melody, and vertical or harmonic if it pertains to simultaneously sounding tones, such as in a chord.
Beat The beat is the basic unit of time, the pulse (regularly repeating event), of the mensural level (or beat level). The beat is often defined as the rhythm listeners would tap their toes to when listening to a piece of music, or the numbers a musician counts while performing, though in practice this may be technically incorrect (often the first multiple level). In popular use, beat can refer to a variety of related concepts including: tempo, meter, specific rhythms, and groove.
Measure A measure (or a bar) is a segment of time corresponding to a specific number of beats in which each beat is represented by a particular note value and the boundaries of the bar are indicated by vertical bar lines. Dividing music into bars provides regular reference points to pinpoint locations within a musical composition.
Solfege Solfege is a music education method used to teach pitch and sight singing of Western music.