No matter how slight the limp, your cat is limping because walking normally and applying full force to the limb hurts.
Cats can limp for many reasons. Active or heavy pets can twist and strain things just like humans do. Cats can misjudge jumps and fall off of things, they can also jump or run and twist or turn a joint in a manner that causes temporary discomfort. Most lameness or injury caused by acrobatics are short-lived. They arrive suddenly and disappear within a day if not a few hours. In most cases, simply restricting activity will solve the problem.
If limping/lameness continues for more than a day or so, had a gradual onset or is severe enough that the pet is uncomfortable, then it’s time to see your veterinarian.
Limping can be a sign of:
Abscess or puncture in the foot
Abscess or puncture higher on the leg
A broken bone
A torn ligament/tendon
Structural damage or deformity
Muscles strain or injury
An unseen bruise or cut
Issues caused by declawing earlier in life
Certain cases of limping are considered an emergency: Possible fracture, hit by car, attacked by larger/bigger animal, bleeding, any signs of collapse, or a possible snake bite should be seen immediately.