From latin centum meaning one hundred.
A period of one hundred consecutive years.
In Roman times a century was a group of one hundred soldiers that were controlled by a centurion. Today we use it to mean one hundred consecutive years. At the moment we are in the twenty first century A.D. Here we are counting centuries in periods of one hundred years dating from the birth of Jesus. Time before this event is measured in centuries B.C. If neither A.D. or B.C. is used then we normally understand the date to be A.D.
For example: The last ice age finished about fifteen thousand B.C.
This pottery has lain undisturbed for five centuries.
This building dates from the thirteenth century.
The industrial revolution started three centuries ago.
A century is also used in cricket to talk about a batsman or a team scoring one hundred runs. Two hundred runs is called a double century.
For example: "This is the batsman's third century this season."
"The batsman hits a four and that brings up his century."