Posthitis: Inflammation of the prepuce (the foreskin of the penis).
In the uncircumcised male, posthitis and balanitis (inflammation of the glans, the rounded head of the penis) usually occur together as balanoposthitis: inflammation of both the glans and foreskin.
Circumcision prevents balanoposthitis. Without a foreskin, there can of course be no posthitis and hence no balanoposthitis.
An uncircumcised boy should be taught to clean his penis with care to prevent infection and inflammation of the foreskin. Cleaning of the penis is done by gently, not forcibly, retracting the foreskin. The foreskin should be retracted only to the point where resistance is met. Full retraction of the foreskin may not be possible until the age of 3 or more.
The term "posthitis" (pronounced pos-THI-tis) comes from the Greek "posthe" meaning foreskin + "-itis" meaning inflammation = inflammation of the foreskin.