Complex sentence: In Philosophy, as well as field such as Ethology, a Proximate Cause is a cause which immediately proceeds something, as opposed to an ultimate cause, normally thought of as the "real reason" something occurred.
Split into simpler sentences: In Philosophy, as well as field such as Ethology, a Proximate Cause is an event which is "closest", or immediately responsible, for producing some observed result. This exists in contradistinction to a higher-level "ultimate cause" which is usually thought of as the "real reason" something occurred.