In simple terms, it's a small modification to a model which usually produces some kind of specific change, commonly an art style, a pose, a hairstyle, something like that. This link describes it in more depth: https://softwarekeep.com/help-center/how-to-use-stable-diffusion-lora-models
You can find lots of them here: https://civitai.com/
If you see a 'Lycoris', it's like a fancier lora.
This is really cool. One of the first things I tried to do when image generation came around was to make a story book, but the characters changed too much between prompts. Loras seem to fix that.
Or you could just use it to make regular image set yeah? That will be awesome when we can have galleries where the models go from clothed to fucked etc.