When computing the series expansions, you get expressions with one of the terms represented as the Landau symbol O. This term shows the truncation order (error order) of the computed series expansion.
MuPAD® automatically simplifies the O-term:
O(10*x^7 + 20*x^8), O(x^2 + x + 1), O(x^3*y^2 + x^2*y^2)
When evaluating expressions with order terms, the system uses standard arithmetical operations for these terms:
O(x^3)/O(x^2), O(x^3) + O(x^2), O(x^3)*O(x^2)