A breadcrumb trail is a set of links that shows where a user is located in relation to other pages of the store.
Home > Gear > Fitness Equipment are the breadcrumbs for Fitness Equipment Category of the store.
The breadcrumbs can be configured on catalog pages and on CMS content pages.
The breadcrumb can look different on different themes, but they usually are displayed in the upper-left corner.
How to enable / disable breadcrumbs?
Go to Stores > Configuration > (General) > Web
And in “Show Breadcrumbs for CMS Pages” select Yes or No.