There are two basic situations where the person after the opening bidder will make a takeout double: 1) Where the doubler expects to be the dummy, and 2) where the doubler expects to be the declarer.
The answer to the question is YES in the first case. After the opening bid, the second person ("seat") will double to show strength in all the unbid suits, with an average of four cards in each of these suits, and maybe a singleton in the opener's suit (occasionally a doubleton or a void). Such a call indicates that my length and strength in each of the unbid suits is reasonably close to the "average" of four. "Three" would fit this average, two would not. The meaning is, "if you bid your best suit and I am dummy, we should be able to make a low level contract if the opponents don't have a game. If they do, the penalty for our going down would be less than the score they would make for game.
In the second instance, the caller has a hand of 16 points or more with a five card (or longer) suit that is stronger than that of either the typical doubler or overcaller. Such a person wants to be declarer. In that case, the correct sequence of bids is for them to double first, then overcall. This overcall (the second thing said), doesn't require three cards in every suit (specifically yours), because it can override your bid. Instead, the doubler wants information about your hand, before going their own way. If you have an unusually long suit or support for the doubler's suit, you will be pleased to know that the doubler has "extra" strength beyond that of most doubles.