''Septa'' means Seven, so a polygon which have 7 Angles, 7 Sides and 7 Vertices is known as Septagon.
Septagon is also known as Heptagon.
Below figure represent, Septagon PQRSTUV.
In the Above Figure 1 :
Septagon PQRSTUV has
7 Sides  PQ, QR, RS, ST, TU, UV and VP
7 Angles  PQR, QRS, RST, STU, TUV, UVP and VPQ
7 Vertices  P, Q, R, S, T, U and V
Below figure represent, Septagon ABCDEFG.
In the Above Figure 2 :
Heptagon ABCDEFG has
7 Sides  AB, BC, CD, DE, EF, FG and GA
7 Angles  ABC, BCD, CDE, DEF, EFG, FGA and GAB
7 Vertices  A, B, C, D, E, F and G.

