The Picard variety of a smooth projective variety 
over 
is the Abelian variety
parametrizing line bundles algebraically equivalent
to the trivial bundle. Writing 
for the group of Weil
divisors algebraically equivalent to zero and 
for its subgroup of principal
Weil divisors, its complex points form 
. The Albanese
variety is the dual Abelian variety of
the Picard variety.
Two line bundles on 
are algebraically equivalent when, up to isomorphism,
they can be joined by a finite chain of families over
connected schemes of
finite type over 
.
A family over 
is a line bundle on 
; its restrictions over two complex points of 
give one step in the chain. Weil
divisors are algebraically equivalent when their associated line
bundles are algebraically equivalent (Kleiman 2005, pp. 41-42).
