.

Used to end a sentence.
Also, period, full stop, dot and bullet point.
When three .'s are next to each other (i.e. ...) it means a pause, you don't know what to say or used in books to start a new idea.
Teachers are nuts about them.

Day 1
Teacher: Your sentences are to long, use more .'s.
Student: Yes Mr.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Day 2
Teacher: Your sentences are to short!
Student: Geez, make up your mind.