Concrete category
Collection
definiendum
$\langle\!\langle {\bf C},F\rangle\!\rangle$ in it
inclusion
$\bf C$ … locally small category
inclusion
$F:{\bf C}\longrightarrow{\bf Set}$
inclusion
$F$ … faithful
Reference
Wikipedia:
Concrete category
Subset of
Locally small category
Requirements
Faithful functor