– a misspelled version of sir meant to politely disagree with someone else online. It can be used in the same places as a traditional sir or ma'am, but with total disregard for potential gender bias. Ser is meant to politely disagree with any gender, noun, bot, adverb, vowel, or any other acceptable, unacceptable, or unknown entity expressing it's (or their) own opinion.
Some use it without disagreement however.
Ser, please read the Bitcoin whitepaper, considering you just said 'i think i can day trade bitcoin for an income'