Let's say you go out with your boyfriend/girlfriend three times a week, is it correct to use the word date? Or another word is more appropriate?
There is no right or wrong on this.
New couples who are in the early stages of a relationship tend to refer to the "first date", "second date", and so on. But once the relationship is "confirmed", or "official" they tend not to use the term to describe every occasion that they meet. It may be reserved for especially romantic meetings such as dinner in a restaurant or appearing together at a party. Some may cease to use the term at all.
In British English couples tend to use the expression "going out" to describe a couple that are regularly dating (eg "John and Jane are going out") or to informally describe a date they are going on themselves ("we are going out tonight").
However, couples who have been together long-term often use the term "date night" to describe specific occasions where they have set aside time to go out together in a formal or casual setting.
There are clearly trends that dictate its use, but I don't believe that anybody would call you out for "misuse" of the term - nobody would find it unusual to use the term at any stage of a relationship.