Kolmogorov complexity defines the complexity of things in terms of how many bits it takes to specify them.
All integers can be specified using a finite number of bits, proportional to their logarithm.
Similarly all rationals can be described using finite bits of precision, by describing their numerator and denominator.
All algebraic numbers can be too, by describing the polynomial they are the root of, and then assigning an order to all the roots, and indicating their index in that order.
Even transcendental numbers like pi and e can be described using a finite number of bits, whether by describing their definition, or e.g. the Taylor series that generates them.
But only a countably infinite number of reals can be described using a finite number of bits (no matter in which language). There's uncountably infinite reals, so most reals cannot be described in a finite number of bits at all.
Is there a name for such reals?
Looks like it's (un)defineable number, as I found out after using different search terms 2 minutes after I asked this.