formal sum

plural formal sums

1. An expression which looks like a sum but where the symbol + has a purely symbolic role, in the sense that the summands cannot be meaningfully combined.
   1. algebraAn element of a free abelian group or vector space regarded as a sum of basis elements.
   2. mathematicsA sum of an infinite sequence of numbers considered as an indeterminate object, in the sense of being subject to certain algebraic manipulations but not necessarily convergent.