Intervals
An interval is "something from here to there". A part of something that we pick.
In mathematics, an interval, for example, an interval in a line of numbers, will represent a section of that line.
Intervals can be closed, open, or half-open. They are denoted by parentheses or brackets, with their respective starting and finishing points, called the endpoints.
A closed interval is an interval that is defined between those endpoints and includes the endpoints too. It is denoted by brackets:
An Open Interval is an interval that is defined between those same endpoints, but does not include the endpoints. In this case, the brackets face outwards.
Example: