If I need to choose between,

Black 3/4 leggings - High waist tights
and
Gym Tights Black with Red Banding SUPPLEX Fabric For Comfortable Fit

I'll name my URL,
buymystuff.com/black-3-4-leggings-high-waist-tights

and in the title, I'd write "Black 3/4 Leggings - High Waist Tights" and the description of the product (and also on the meta description) I'd have, "Gym Tights Black with Red Banding SUPPLEX Fabric For Comfortable Fit"

And do go to Google Keyword Planner to check what are the most searched keywords for the product above in your country. You create a Google Adwords without a credit card, watch this tutorial, https://www.youtube.com/watch?v=6n8PWPDf4kk&t=26s

Hope this helps.