  This paper has two aims. The first is to give a description of irreducible
tempered representations of classical p-adic groups which follows naturally the
classification of irreducible square integrable representations modulo cuspidal
data obtained by C. Moeglin and the author. The second aim of the paper is to
give description of an invariant (partially defined function) of irreducible
square integrable representation of a classical p-adic group (defined by C.
Moeglin using embeddings) in terms of subquotients of Jacquet modules. As an
application, we describe behavior of partially defined function in one
construction of square integrable representations of a bigger group from such
representations of a smaller group (which is related to deformation of Jordan
blocks of representations).
