I used to have to mail out a lot of catalogs and promotional literature packets for my business. I was working from home, so I would just carry these packages to the post office a few times a week. I always use sent them regular mail, until one day the clerk asked me what was in these packages I was always sending. When I told her, she starting sending them at media rate. Saved me some money.
For those who don’t remember the changes to bulk mailing costs in the 1990’s here is a mapping from the earlier USPS classes to the more modern terms.
Second Class -> Periodicals
Third Class -> Standard mail A
Fourth Class -> Standard mail B
On January 7, 2001, the USPS renamed “Standard Mail A” to just “Standard Mail.”
It also renamed “Standard Mail B” to “Parcel Services.”
Source: https://www.federalregister.gov/documents/2000/12/15/00-31357/changes-to-the-domestic-mail-manual-to-implement-docket-no-r2000-1
Search on the page for “name change”.
In January 2017, it changed “Standard Mail” to “USPS Marketing Mail.”