Is buying price same as selling price?

Excuse me, I'm a bit confused about something. Could you please clarify for me? When we talk about buying and selling prices in the world of cryptocurrency or finance, are they always the same? Or is there some kind of difference between the two? I've heard some people mention spreads and slippage, but I'm not entirely sure how those factors come into play. Could you elaborate on this for me, please? Thank you in advance for your help.