The Collaborative International Dictionary of English v.0.48:

Encapsulation \En*cap`su*la"tion\, n. (Physiol.)
   The act of inclosing in a capsule; the growth of a membrane
   around (any part) so as to inclose it in a capsule.
   [1913 Webster]

WordNet (r) 3.0 (2006):

encapsulation
    n 1: the condition of being enclosed (as in a capsule); "the
         encapsulation of tendons in membranous sheaths"
    2: the process of enclosing (as in a capsule)

The Free On-line Dictionary of Computing (30 December 2018):

encapsulation

   1. The technique used by layered protocols in which a layer
   adds header information to the protocol data unit (PDU) from
   the layer above.  As an example, in Internet terminology, a
   packet would contain a header from the physical layer,
   followed by a header from the network layer (IP), followed by
   a header from the transport layer (TCP), followed by the
   application protocol data.

   2. The ability to provide users with a well-defined interface
   to a set of functions in a way which hides their internal
   workings.  In object-oriented programming, the technique of
   keeping together data structures and the methods (procedures)
   which act on them.

   (1998-09-07)