They air in the morning or during early evenings and typically run for 100-150 episodes. They tend to be slow-paced and packed with many different characters (you might need to have a relationship chart in handy, especially since several plotlines might run in a single episode).

Most daily dramas are in the family drama genre, although the KBS morning drama slot (TV Novel) belongs to the period drama genre (they are set in the 1940s-1980s). MBC used to air daily sageuk, but they discontinued it, probably due to the cost.

Daily dramas have earned a bad reputation due to tired, cliched plot (they mostly focus on adultery or birth secrets). A few good ones do exist. Personally, I'm fond of the ongoing "My Dear Cat" (which "It Must Be Love" will replace most likely in November, not January as reported). It's slow-paced, light and low-key, but despite its usage of cliched tropes, it still has its own identity and freshness. The characters are in no way paper-thin; all have their own set of flaws and redeeming values. Choi Yoon-young is such a delight in that drama and plays the awkward, quirky writer character very well.

I'm not that familiar with daily dramas, but I watched King's Daughter Soo Baek Hyang, because I heard so many good things about it and I totally recommend it! It's one of the daily sageuks by MBC that Dakchigo mentioned and was basically like a long historical drama just with shorter episodes (~30 mins), so you'd spend about the same time as when watching a ~50 episode sageuk.

The only other one I watched is Vampire Idol, which was like a sitcom where episodes can be watched more or less independently from each other (aside from the overarching story developments). Personally I found it hilarious, but it's also pretty low budget and not fully subbed yet, so lots of people will probably skip it.