quick question what does the 220 mean in a TO 220 package

[generic_username]

As the title says I can't seem to find any Information for what the number in a TO package means.
cheers.

[Gyro]

Nothing exciting I'm afraid. It's just its numerical designation under the JEDEC international package standard... Google JEDEC.

[coppice]

TO == Transistor Outline
220 == The one that came after 219 at the JEDEC meetings.

TO3, TO5, TO18, TO220. We remember the golden oldies, and forget all the rest. 

[Gyro]

Err... TO92, SO, SOT etc.? 

Edit: But yes, we didn't see or remember all the ones in between. 

[GNU_Ninja]

TO archive: https://www.jedec.org/standards-documents/focus/registered-outlines-jep95/transistor-outlines-archive 

[generic_username]

wow big thanks to everyone, didn't know that there's no meaning for that naming

[T3sl4co1l]

There are some crosses, like:
TO-3 superseded(?) by TO-204.
TO-220 royally sucks; TO-220AB is more familiar.
TO-5 is the really old (large can) one, but it's potted; TO-39 is actually the welded can version.  And TO-99 is the multipin version.
TO-72 is the four pin TO-18 (which are potted as well, or at least usually).

Almost every time someone says "2Nxxxx" and it's a TO-18 part, they're being dumb.  No one buys 2N2222s anymore, nor should they.  PN2222 is the plastic (TO-92) variety, but even better is 2N3904 or 2N4401 (a much better spec'd general purpose BJT).

Or in reference to avalanche pulse generators, 2N2369 is a pretty awful choice, but the PN (TO-92) or MMBT (TO-236 aka SOT-23) variant is pretty good.

Tim