What does the resistance in an electrical circuit limit?
Current flow. It's also worthy of noting that a resistor doesn't
limit-by, it limits-to, and the current is dependent on the
voltage.
I[A] = U[V] / R[ohm]
It's also worth to note, that the power flowing through said
resistor with resistance R is I[A] * U[V] for DC circuits - helps
to remember this well when picking appropriately-rated resistors
for replacement.
Example: let's say we have a 20-ohm, 2W resistor. If we place it
in a circuit with 5V, we will get 5V / 20ohm = 250mA (0.25A) of
current flowing through the resistor. The power the resistor will
"see" is 250mA * 5V = 1.25W, so it's safe.
But let's now put that same resistor in a 12V circuit. The
current flowing will be 12V / 20ohm = 600mA (0.6A), and the power
will be 600mA * 12V = 7.2W, so the resistor will burn.