Note: This is in no way exhaustive. Just some terminology I'll be using in my LMP project.
Works where only one instrument is playing a particular part. Like a string quartet where there is one violin playing the first violin part, one violin playing the second violin part, one viola, and one cello.
Works where multiple instruments are playing any given part. So if there are 15 first violins, 15 second violins, 7 violas, 7 cellos, and 4 basses, that's an orchestral work. Early on (like early 1700s (check dates)) they'd just take a Chamber Work and make it into an Orchestra Work by having multiple instruments play the same part, but eventually composers started writing pieces explicitly for orchestras.
General Note: Tempo is the speed at which you play a piece. Generally, chamber music tempos are indicated by Italian words, regardless of the composers national origin. So even a work by Beethoven or Brahms (both Germans) will use the Italian "Allegro" and "Andante" etc. This list isn't exhaustive; it's just some common ones.
Beats Per Minute. 60 BPM is one beat a second, 120 is 2 beats per second etc. The tempos below have a range of BPMs that's a bit... fuzzy. A metronome will have allegro as between 110-120 BPM, but most scores don't specify a specific BPM. They'll just say "Allegro" and it's up to the performers (or conductor) to decide how fast that is.
Fast ( around 110-130 BPM)
Not quite allegro (around 100-110)
Walking pace (around 75 bpm)
Really fast (around 170 bpm)
Really, really, like "f*ck you" fast (200 bpm and up)
Moderately fast (around 90 bpm)
Slow (around 60 bpm)
Very slow (around 50 bpm)
Minuet - Trio
This form came out of french Baroque dance. It's in 3 (think waltz) and has the large scale structure of A-B-A, with A being the Minuet and B being the Trio. Originally the Minuet was scored for the whole ensemble, and the Trio was cut down to just three instruments. Even when the instrumentation convention changed in the Classical Era, the name Trio stuck. The return to the Minuet (A) after the Trio has the effect of "bringing the music home" and giving it closure.
Theme and Variations
Exactly what it sounds like it is. It'll have one theme and then start to modify that theme with each variation. The theme is usually still pretty recognizable.
Mozart's "Variations on "Ah, vous dirai je maiman" (i.e. "Twinkle Twinkle Little Star") is an example.
A form where a short melody idea in multiple "voices" being introduced one at a time and then interweaving. (A voice isn't a human voice, it's just a term that means a separate part / melody line. Same principle as a four part harmony barbershop quartets, but each part is instrumental in this case.)
Bach's Little Fugue in G Minor makes it really easy to hear and (in this case, see)
Really popular form with multiple themes being connected by non-thematic material. Usually structured as Exposition - Development - Recapitulation - Coda. The Exposition is where the themes are established, the Development is where the composer disassembles and mucks about with the material, the Recapitulation is where the themes return and the Coda is the ending.
Note: A "Sonata" is also a piece that is written for either a solo instrument or a solo instrument with an accompaniment like a piano. For maximum confusion, this kind of Sonata is not necessarily in sonata form, and plenty of non Sonatas are in sonata form.
One main theme that alternates with contrasting themes called episodes. They're structured something like ABACA, with A being the main theme and B and C being episodes.
Fur Elise by Beethoven is a Rondo.
Soft. Notated on the score as "p"
Really soft. Notated on the score as "pp"
Moderately soft. Notated on score as "mp"
Loud. Notated on the score as "f"
Really loud. Notated on the score as "ff"
Moderately loud. Notated on score as "mf"
Get gradually louder. Notated on score as "<"
Get gradually softer. Notated on score as ">"