pking boosting is where you exploit issues with the game intentionally to raise your kill count very quickly, such as constantly having someone run out of the water and spamming your sword.
Spar boosting is intentionally letting someone win a spar repeatedly to improve their rating and record.
both individuals get punished for boosting. There is a custom script to detect boosting that gives admins a notice, to which they then verify it is actual boosting. I think its like 15 pks on a row on the same person and 25 spars in a row on the same person, but they have tweaked the numbers or the system.