KV means key value. Essentially the suggestion is to organize your data as a big key value structure(hashmap-like).
This term usually means data is not normalized/separated as in regular SQL.
for instance, in SQL:
User table, that has columns: id, email
Article table, that has columns: id, text, user_id
KV/noSQL equivalent:
Article document, that has properties: id, text, user_email
for instance, in SQL:
User table, that has columns: id, email
Article table, that has columns: id, text, user_id
KV/noSQL equivalent:
Article document, that has properties: id, text, user_email