Theoretically, yes .... practically, no (at least for the moment).
The HTML tag that forces a line break (I think of the "br" as meaning "break" - it helps remember the tags when I associate a word with them that suggests their action) used to be <br>. When HTML version 4 came out, it changed that to <br />.
The reason for this is that almost all HTML tags are containers - there is a start tag and an end tag. When you use them, all content in between the start and end tags is what the tag meaning is applied to. For example: This is <b>bold</b> text would display with the word "bold" in bold font.
A very small number of HTML tags do not have end tags - <br> is an example, with <hr> (for "horizontal rule" - it places a line across the page) is another example. In order to be more consistent, the rule was made that ALL tags MUST have a start and end. For cases where tags are not containers, the tag is changed to sort of incorporate the start and end tags all in one by adding the "/" before the end.
Right now, all browsers support the current version as well as most tags in previous versions (they are backwards compatible). At some point, however, they will stop supporting the old versions - if that ever happens then <br> will not be interpreted by a browser, so it is good to use the currently supported set of tags.
I bet you're sorry you asked!