a proportion in relation to a whole (which is usually the amount per hundred)
"Only about ten percent of the applicants were selected for the final round of interviews."
Wikipedia
"The article notes that according to recent data, approximately fifty percent of the population supports the new policy."
In plain English: A percent is a way to show a number as parts out of 100.
"The sales tax is five percent on all groceries."
Usage: Use "percent" as a noun to refer to a specific portion expressed per hundred, such as in "a small percent of voters." It functions grammatically like any other singular countable noun and requires an apostrophe only when forming the possessive (e.g., "the percent's value").
For every hundred (used with preceding numeral to form a noun phrase expressing a proportion).
"Only fifty percent of the applicants passed the final round of interviews."
In plain English: Percent is an adverb that means something happens to a certain degree or extent, often used to describe how much of a change occurred.
"Only a few percent of the voters showed up to cast their ballots."
Usage: Use "percent" as an adverb only after a number to indicate that something happens in relation to every hundred items or units. Place it directly following the numeral without adding the word "of," such as saying "The price increased by ten percent."
Per hundred.
"The survey results showed that exactly twenty percent of the voters preferred the new policy over the old one."
The word percent comes from New Latin per centum, which literally means "by the hundred." It entered English to describe a ratio or percentage based on that unit.