A semicolon is a punctuation mark that looks like a comma with a dot above it (;). It is used to separate two closely related independent clauses that are not joined by a coordinating conjunction.
When a sentence has multiple commas, using a semicolon can help clarify the separation between items in a series and prevent confusion. It indicates a stronger break than a comma, but not as strong as a period.
Example from page 2:
"The equipment needed for the hiking trip included backpacks, tents, sleeping bags, cooking utensils, and extra clothing; the group made sure to pack everything carefully."
In this example, the semicolon clarifies the separation between the items in the series (backpacks, tents, sleeping bags, cooking utensils, and extra clothing) and the following independent clause.