Seattleites are extremely nice and considerate, but are often reluctant to actively make new friends or be genuinely warm towards people. It is a type of cool introversion found especially in the Puget Sound area, but experienced in Washington State in general.
This term might be used between a couple of people who have just moved to Seattle, and are confused by our way of interacting.
Jill: Yeah, so I said to her that I was going to Bite of Seattle this weekend, and if she'd be interested, that I had an extra ticket.
Kelly: It's cool you're meeting people. I've been here for a month, and I've had a really hard time.
Jill: No, wait. We had been chatting up to that point, with the best vibe, and I said that maybe we could hang out some weekend, if she wasn't busy. She said that that would be great, and the moment I suggested Bite of Seattle, she was all, “Yeah, maybe so,” and excused herself to go to the bathroom.
Kelly: Man, that is so typical of people here. You just got the Seattle Freeze. I don't know how I'm gonna adapt to this place. At least the coffee's good.
This is a pretty new term, coined in the early 2000s. It is used by young Seattleites in-the-know and out-of-towners who discover it by firsthand experience. Possible causes of the Seattle Freeze include the weather itself, the amount of people who work in the tech industry (who tend to be a shy, introverted bunch), and the large population of Scandinavian immigrants (who originate from a more reserved culture).
Here's someone who has found a way to get around the Seattle Freeze: