Musical Forms and Compositional Types
Classical forms
Khayal: a bandish in sthayi and antara, with alap, taan, bol-bant and sargam improvisation; vilambit and drut. Dhrupad: sthayi, antara, sanchari, abhog; pakhawaj; nom-tom alap; austere raga treatment. Dhamar: 14-matra pakhawaj form, often a holi theme, with more rhythmic play. Tarana: fast syllable-based composition (nom tom, daridra) with no literal meaning.
Instrumental and light forms
Gat: instrumental composition in sthayi/antara, commonly maseetkhani (vilambit) and razakhani (drut). Thumri: light classical, Braj lyric, dadra/keharwa, bol-bana and expression over extended alap. Bhajan: devotional, strophic, accessible. Film and light music may borrow ragas and talas but follow cinematic, not raga, structure.
Worked example
Compare khayal and thumri in the same raga. Khayal states a bandish, then develops raga through systematic alap and taan; thumri keeps the raga light, expands the lyric's emotional suggestion, uses bol-bana, and allows rhythmic flexibility. The difference is not 'classical versus folk' but structural: khayal develops raga, thumri develops bhava.
Traps
Saying tarana has meaningful lyrics; confusing dhamar with dhrupad; calling a gat a bandish; treating film songs as raga compositions; describing thumri as fast khayal.