It's $3k period, for offsetting normal earned income. There is no cap on offsetting capital gains (for example, from selling stock). And you can do both, e.g. wipe out for example $20k in capital gains then another $3k in normal income.

I told a business at a $60k loss 4-5 years ago and between capital gains offsets and normal income deductions I still have about $30k in deductions left.