Your phone makes the message beep. You open and check and it reads “Wow, you have won yourself 1 million naira in the ongoing 'blablabla' promo. To redeem your prize, call me now”. You knew you didn’t participate in the promo, infact, you never bought their product. That’s a spam message.
You have one message received. So your phone reads. You open and find a long text about something that doesn’t really interest you from someone or a number you don’t recognize, and at the end of the write-up you find “Send this to 20 persons today and get rewarded with 'sososo' amount of money”. You are a recipient of a spam message.