''Penta'' means Five, so a polygon which have 5 Angles, 5 Sides and 5 Vertices is known as Pentagon.
In the Above diagram :
Pentagon ABCDE has
5 Sides  AB, BC, CD, DE and EA
5 Angles  ABC, BCD, CDE, DEA and EAB
5 Vertices  A, B, C, D and E
In the Above diagram :
Pentagon PQRST has
5 Sides  PQ, QR, RS, ST and TP
5 Angles  PQR, QRS, RST, STP and TPQ
5 Vertices  P, Q, R, S and T

