In some contexts, the presence or absence of a trailing slash can change the behavior of a web server or the way that a URL is interpreted.
For example, consider the following two URLs:
https://www.example.com/path/https://www.example.com/path
The first URL has a trailing slash, while the second one does not. Depending on how the web server is configured, these two URLs could refer to different resources or could behave differently. In some cases, adding or removing the trailing slash can cause the web server to issue a redirect to the same resource with the trailing slash added or removed.
Why it’s called “trailing”?
The term "trailing" refers to the fact that the slash appears at the end of the URL, following the rest of the characters. It is called a "trailing" slash because it trails after the rest of the URL.
The term "trailing" is often used in computing to describe something that appears at the end of a string or other data structure. For example, a trailing space is a space character that appears at the end of a string, and a trailing newline is a newline character that appears at the end of a string.
(/) that goes at the end of a web address. The word "trailing" just means that it's at the end.