Can someone help inform me better: I heard there are no significant mutations yet, but I also heard there are 2 "strains": S-cov and L-cov, where S-cov is a mor

Can someone help inform me better: I heard there are no significant mutations yet, but I also heard there are 2 "strains": S-cov and L-cov, where S-cov is a more recent and less dangerous variation. Is this right?