Deacon is a broad catch-all term — range of roles with varying authority, all below elder

Deacon (diakonos) means servant but in an official sense. Some deacons may have more authority than others, but none have as much as an elder. It doesn't include teaching with authority. Examples: running audio/video, handling finance and tax paperwork, running the food ministry, overseeing church picnics, coordinating helps ministry. Deacons have lots of variety in authority level but are not elders.