Word used all the time by most people
Often wrongly translated to 'cosy', but it's much more than that. 'Gezellig' is anything with a good social vibe, being in good company, having a good time. You need other people for it to be 'gezellig'.
"Dankjewel voor je leuke feestje! Het was weer gezellig!"
Thank you for the wonderful party! It was gezellig!