What does an apostrophe signify when used after 's'?

An apostrophe used after 's' signifies possession in the context of plural nouns. When 's' is placed at the end of a noun form that already has an 's' to indicate plurality (such as "dogs" or "cats"), adding an apostrophe after the 's' indicates that multiple entities possess something. For example, "the dogs' park" means the park belongs to multiple dogs. This usage clearly conveys that the ownership is shared among the plural subject.

In terms of the other options, a contraction involves combining words, which would typically not involve an apostrophe following 's' in this context. A complete sentence is determined by grammatical rules, not the use of apostrophes, and an apostrophe does not indicate a plural form of a word; rather, the plural is formed through other means, such as adding 's' or 'es' without an apostrophe.