Anything that refers to a previous generation of a subject/idea/object/etc. Typically, they are highly regarded and sometimes the very thing that started it all.

To use paper currency instead of a credit or debit card

from back in the day

A positive appellation referring to when things weren't flashy but empty of substance, were done by hard work, didn't pander to the lowest common denominator, and required real skill. Labour-saving devices, shortcuts that reduce quality and quitting before the task is done are not characteristics of "old school."

In reference to computer games, refers to a game that had substantial playability without flashy graphics or eye candy. Old school gamers appreciate difficult maneuvers, careful planning, and scorched earth policies.

In reference to role-playing games, old school refers to games that tested players' wits, could kill off careless characters, and required dedication and inner strength to play. Old school games didn't pander to the ideas that everyone is created equal, that all options are open to all races, that the markets were somehow free, and that a quasi-medieval society could have near 100% literacy.

See also classic.

1) Retro
2) As Before (as something was done, said, etc.)

The way things used to be done.

A term used by many young people and liberal older people use to describe people over 50 with a stern or formidable personality that believe in harsh discipline and no coddling thinking that being that way will produce a good citizen and a better person. Many old school men believe in hard work for success, women that are not housewives should work only in occupations such as teaching, secretarial work, or nursing, children need to be put in their place and not part of adult conversation, smoking cigarettes and drinking alcohol is okay, but marijuana is horrible, and that making a man out of a young boy is not having a deep conversation followed by hugs or tears.

1. Music from back in the day, the last decate and before.
2. A. Some thing that past is time or it's fashion, or
B. a bring back memory of of a thing in the respectable way.

The term old school is of English origin and dates back to at least the 19th Century and is used to denote something that is considered to be out of date with currents trends/ideas and thinking. An early example of the term can be found in the Charles Dickens novel Bleak House (first published 1852).