Simple Definition:

Punctuation is a set of marks used in writing to clarify meaning and indicate pauses or emphasis [giving special importance or attention to something].

For example:

• The period (.) is used to end a sentence. [Period means a small dot used at the end of a sentence.]
• The comma (,) is used to separate items in a list, or to indicate a short pause in talking. [Comma means a small curved mark used to separate words or phrases in a sentence.]

Very Simple Definition:

Punctuation is a group of marks (symbols) used in writing to help us understand and read sentences better.

For example:

• A period (.) means the end of a sentence.
• A comma (,) is used to separate words in a list.