The act of flirting with any girl within three feet. Usually out of pure desperation for some action, someone who "seidls", or undergoes the act of Seidling, will flirt and hit on anything with a vagina, even if the girl has a boyfriend.
Q:""Hey why is that kid hitting on my girlfriend?"
A: "Oh don't worry, he's just seidling"
Q: "How desperate for action ARE you?!"
A: "I'm so desperate i have to resort to seidling"