What is the term for an acutely presenting, erythematous, tender lump within the eyelid?

The term for an acutely presenting, erythematous, tender lump within the eyelid is hordeolum, commonly referred to as a stye. This condition occurs when there is an acute inflammation of the glands located in the eyelid, typically resulting from a bacterial infection. Patients often experience pain, swelling, and redness localized to the eyelid, which can be quite uncomfortable.

Blepharitis involves inflammation of the eyelid margins but is usually chronic, rather than the acute presentation seen in a hordeolum. A chalazion is a painless bump resulting from a blockage of the meibomian gland and is not typically tender or erythematous, distinguishing it from a hordeolum. Iritis refers to inflammation of the iris within the eye and does not specifically describe a lump in the eyelid. Thus, hordeolum is accurately defined as the condition presented in the question.