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.

As has been pointed out, most if not all adjectives presuppose a reference system whereby their appropriateness in describing a referent is judged.

Sometimes, this will call for a subjective decision - where does green end and yellow begin?

Classifying and 'singling out' adjectives such as chemical, unique, solar are inherently ungradable, but may still be contrasted with adjectives referring to related classes (physical; lunar).

Those terms which apply to a referent when viewed in one reference system, but not when viewed in others (such as short / long above) are context-dependent - a descriptor hardly confined to grammar, but very appropriate.

I guess you're thinking of a grammatical unit native to another language. I imagine some other languages can have a particular term.

But in English, the words that you cited are all just classified as "adjectives."

Relative properties start when we employ comparative and superlative forms of adjectives. But they're already different from what you want to identify. For example, faster, longer, stronger etc.

Words that you might find helpful are:

attribute 

property 

But I have to tell you that they're not really limited to grammar terminology.

There has been an argument among English prescriptive grammarians about whether you should be able to use comparatives on adjectives like perfect, just, dead, unique. It seems that logically, they shouldn't be able to take comparatives¹, but English speakers persist in using more perfect, more just and juster nevertheless. Googling this set of adjectives, you find that they have been called absolute or ungradable. Adjectives not in this set would then be relative or gradable.

Since English speakers go ahead and apply comparatives to all adjectives, it isn't clear that this is a real grammatical class in English.

¹ If something isn't perfect, it has to be imperfect, so it can't be less perfect. Similarly, unique means there is only one of them. If there are two, it's no longer unique. And someone is either dead or alive; how can one person be more dead than another?