Another critical understanding that you're missing - the "relational" part in an RDBMS isn't for the table - it's for both the row and how rows in different tables relate.

"Relational" comes from "A Relational Model of Data for Large Shared Data Banks" which says

The term relation is used here in its accepted mathematical sense. Given sets S1, S1, ···, Sn, (not necessarily distinct), R is a relation on these n sets if it is a set of n-tuples each of which has its first element from S1, its second element from S1, and so on. We shall refer to Sj as the jth domain of R. As defined above, R is said to have degree n. Relations of degree 1 are often called unary, degree 2 binary, degree 3 ternary, and degree n n-ary.

That is the origin of the term in connection with databases. A relation is not a row, it is a set of rows and although 2 relations may have columns that correspond as primary/foreign keys it is just a linguistic coincidence that you might call this corresponsdence a "relationship".