Achilles tendonitis presents as a pain in the in the back of the lower leg. We can describe it with different levels of severity: recent (acute) and longstanding (chronic).
An acute or recent injury to the achilles tendon is characterised by inflammation with swelling, redness or pain in the back of the heel. It may also be the result of a flare up of an old injury.
A chronic injury describes a injury that is longstanding, and while painful, does not present with any visible signs of inflammation. The injury has gone through the acute phase already, and has still not healed completely. Usually we consider this 3 months onwards from the time of injury.