Which of the following translates to "protection, defense, guard"?

The term "praesidium" in Latin directly translates to "protection," "defense," or "guard." It comes from the root "praesid-" which relates to the concept of standing guard or providing support and safety. This word is commonly used in contexts referring to military or protective measures, indicating a sense of security and defense.

The other options do not convey this meaning: "memini" relates to memory or remembrance, "coetus" refers to a gathering or assembly, and "nefarius" is associated with wickedness or crime. Each of these terms belongs to different semantic fields, making "praesidium" the only choice that accurately represents the idea of protection or defense.