Clearly there are two different types of character entities in HTML/XML.
There are the ones that are specified by numbers, i.e. < and >
And then there are the ones that are specified by letters, < and >
Is there a specific name for each of these types of character entities, or are they just "character entities that are specified by numbers and character entities that are specified by letters?
These are numeric character references (<) and character entities (<).
Character entities are defined as a sequence of character references - for instance, nbsp is defined as  .
When processed, character entities are converted to the corresponding character references.
By the way - a character entity can be defined as more than one character reference, though this has not been done in XML or HTML.