A "Front line" instrument in a jazz band is usually either Saxophone, Trumpet or Trombone but sometimes also Clarinet, Violin, Flute or Harmonica.
A "Chordal" instrument in a jazz band is usually either a Piano/Keyboard, or Guitar but sometimes also a Vibraphone, Banjo or Accordion.
Some of the most common formats are listed here:
SOLO
1 x Chordal instrument ie. Piano OR Guitar
1 x Frontline instrument ie. Saxophone
1 x Pianist who also sings
1 x Guitarist who also sings
DUO
1 x Chordal instrument and Vocals
1 x Chordal instrument and Doublebass
1 x Chordal instrument and 1 x Frontline
2 x Chordal instruments ie. Piano AND Guitar
TRIO
1 x Chordal instrument, Vocals and Doublebass
1 x Chordal instrument, 1 x Frontline and Doublebass
1 x Chordal instrument, Drums and Doublebass
1 x Frontline, Drums and Doublebass
Piano, Guitar and Doublebass
QUARTET
1 x Chordal instrument, Doublebass, Drums and Vocals
1 x Chordal instrument, Doublebass, Drums and 1 x Frontline
2 x Chordal instruments, Doublebass and 1 x Frontline
2 x Frontline instruments, Doublebass and Drums
QUINTET
1 x Chordal instrument, Doublebass, Drums, Vocals and 1 x Frontline
1 x Chordal instrument, Doublebass, Drums and 2 x Frontline
2 x Chordal instruments, Doublebass, Drums and 1 x Frontline
SEXTET
1 x Chordal instrument, Doublebass, Drums, Vocals and 2 x Frontline
1 x Chordal instrument, Doublebass, Drums and 3 x Frontline
2 x Chordal instruments, Doublebass, Drums, Vocals and 1 x Frontline
2 x Chordal instruments, Doublebass, Drums and 2 x Frontline
Groups larger than a Sextet usually have a "Rhythm Section" of 3-4 members; consisting of Piano AND/OR Guitar as well as Doublebass and Drums. The rest of the group would usually consist of a Vocalist and/or Frontline instruments.
BIG BAND
Piano AND/OR Guitar, Doublebass, Drums
4-5 x Saxophones
3-5 Trumpets
3-5 Trombones