Issuance versus trading between investors.

In the primary market, an issuer creates and sells new assets. Examples include an initial public offering, a follow-on stock offering, or a token launch. The issuer receives capital.
In the secondary market, existing holders trade with one another; the issuer normally does not receive the proceeds.
Key idea: Primary-market activity changes financing and often supply. Secondary-market activity changes ownership and establishes observable market prices.