Slug barrels can be rifled, smooth bore or have a rifled choke, what tends to set them apart from other barrels is the rifle sights on the barrels or mounts for a scope. I've shot quite a few deer with slugs, and all were from smooth bore barrels (mostly modified choked barrels, as that is what my main duck and pheasant shotguns were at the time). The better sights on a slug barrel would be better than what I used back in the day.
The usual difference between a lead and a steel shot capable shotgun is the shotgun a newer shotgun or an old one. Really just about any of the post 1980 shotguns will be steel shot capable, except maybe some of the European shotguns. Steel shot capable barrels are usually thicker (more steel) than the older lead only barrels. An easy example to view would be an old Browing A-5 Belgium barrel compared to a Japanese made barrel.
Turkey shotgun vs. a skeet shotgun - besides the usual obvious Camo, sometimes scoped or with semi-rifle sight vs. wood, blued steel, and a vent rib with a two bead sight system. The main difference is a turkey shotgun normally has some form of full choke - full to extra full, while a skeet gun usually has a skeet choke (which is close to cylinder, but could be as tight as I.C. Turkey loads also tend to be heavy loads with 4, 5, or 6 shot, while skeet loads are light target loads of 8 or 9 shot.
Hope that helps.