The visa-exempt scheme is set by the Thai government, those countries are eligible for 30 days entry stamp for free. This stamp is eligible for 30 days tourism extension.
A visa-waiver is set based on a bilateral agreement, those countries are eligible for
*****
/90 days (depending on nationality) entry for free. This stamp is NOT eligible for tourism extension.
Currently, visa-exempt nationalities can stay up to 60 days without a prior visa but with a tourism extension. Visa waiver (30 days) nationalities can stay up to 30 days only.