In the context of a charm or a bundle, just as in the context of a snap, promotion refers to the association of a revision to a higher-ranking channel risk level of the same track.
For example, in the (partial) output of juju info mongodb below, revision 100 has been promoted from 3.6/edge through 3.6/beta and 3.6/candidate all the way to 3.6/stable. (The up arrow next to 3.6/beta indicates that that channel has been closed and, if you try juju deploy --channel 3.6/beta, what you’ll get is the next higher-ranking risk level of the same track, that is, 3.6/candidate.)
channels: |
5/stable: 117 2023-04-20 (117) 12MB amd64 ubuntu@22.04
5/candidate: 117 2023-04-20 (117) 12MB amd64 ubuntu@22.04
5/beta: ↑
5/edge: 118 2023-05-03 (118) 13MB amd64 ubuntu@22.04
3.6/stable: 100 2023-04-28 (100) 860kB amd64 ubuntu@20.04, ubuntu@18.04
3.6/candidate: 100 2023-04-13 (100) 860kB amd64 ubuntu@20.04, ubuntu@18.04
3.6/beta: ↑
3.6/edge: 100 2023-02-03 (100) 860kB amd64 ubuntu@20.04, ubuntu@18.04
Charm promotion is done at release time by specifying the revision number and the channel [track/]risk level that you want to associate it with (e.g., charmcraft release --revision 118 --channel=5/candidate).