Learn English – A technical term to describe adjectives like “fast”, “long”, “strong”, “large”, “deep”, “loud”, etc

What is the technical term to describe adjectives like fast, long, strong that are used to describe a particular property of an object in relation to another object's?

Here is an example.

Let's say I have a 20-centimetre ruler.

1. I can say,

   This ruler is short.

   as I compare it to a 1-meter ruler.

2. Or I can give the opposite statement as I compare it to my pen:

   This ruler is long.

Both statements make sense. Whether it is short or long depends on what I am comparing it to.

(Edit: counterexamples would be Christian, gravitational, electromagnetic, cosmic, cosmological. These are adjectives, too. And I don't think they fit into the category.)

So what is this type of adjectives technically called?

I've come up with the phrase 'relative term', but after a check with Wikipedia, it doesn't seem to be the technical term I am looking for.

A relative term is a term that makes two or more distinct references to objects (which may be the same object, for example in "The Morning Star is the Evening Star"). A relative term is typically expressed in ordinary language by means of a phrase with explicit or implicit blanks. Examples:
__ loves __
__ is the same object as __
__ is giver of __ to __.

The word is is a relative term when it expresses identity. The colloquial meaning for a relative term is that > it is different for different people. An example: someone who is 5 feet tall might think someone who is 6 feet tall is tall, but someone who is 5 feet 5 inches would think that someone who is 6 feet 5 inches is tall.