toss off is a verb meaning "write quickly". It carries 2 recorded senses.
write quickly
“She dashed off a note to her husband saying she would not be home for supper”
“He scratched off a thank-you note to the hostess”
writing
Definitions, synonyms and semantic relations for toss off come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.