A period is a type of punctuation mark, also called a full stop.
Often, though not always, there is a sense break here, such as a punctuation mark.
It wasn't a threat so much as a punctuation mark.
The knock on the door had been only a punctuation mark.
This page is about the punctuation mark, for other uses, see Period.
In the first two sentences above, only one punctuation mark is used at the end of each.
It was a physical punctuation mark, she decided, separating out the past and future.
Some of his poems can go on for several pages using no more than four words and a punctuation mark.
So he needed a punctuation mark or symbol that did not occur in a name.
Unfortunately, it's not always easy to find those punctuation marks.