B.C, A.D, BCE, CE

B.C.

Before Christ or before Jesus was born

Circa

a latin word that means "about" or "approximately."

Decade

a period of 10 years

Century

a period of 100 years

B.C.E.

before the common era means the same thing as B.C.

A.D.

after Jesus was born

Prehistoric

before the invention of writing

C.E.

common era means the same thing as A.D.

Reign

the length of time a king or queen is in power