Past relates to location and locates something in time (and sometimes in space). It can be used as an adjective, noun, preposition, or adverb.
Past as an Adjective
Definition 1: Gone by in time; elapsed; done with; over.
Definition 2: When attributed to a group of people, it can also mean having served one’s term of office; former.
Example 1: Her days for partying are now past.
Example 2: All past presidents of the United States were male.
Past as a Noun
Definition: The time that has gone by; a time, or all the time, before the present.
Example: In the past, many homes did not have indoor plumbing.
Past as a Preposition
Definition 1: Beyond in time; after; beyond the age for or time of (when stating time of day in minutes, quarter or half hours, or a particular time).
Definition 2: Location; at or on the farther side of (something); up to and beyond (a person or place).
Example 1: It is half past five.
Example 2: My house is the first one past the park.
Past as an Adverb
Definition: So as to pass or go by.
Example 1: The ball sped past Susan’s head.
Example 2: Sylva pushed past the crowd.