Which class of shares have a 12b-1 fee?

Could you please clarify for me which specific class of shares typically carry a 12b-1 fee? I understand that 12b-1 fees are associated with the distribution and marketing expenses of mutual funds, but I'm curious if they're specific to certain types of shares within these funds. Is it the A-shares, C-shares, or perhaps another classification altogether? It would be helpful if you could provide a concise explanation of which class of shares this fee applies to, and any relevant details surrounding it.