Source: 
In the modern bridge world there are a plethora of meanings for various doubles. The two oldest and most used are Penalty Doubles and Takeout doubles. Then there are Support doubles, Negative doubles, Lead-Directing doubles, Suit-Showing doubles, Do-Something-Intelligent doubles and undoubtedly in some dedicated partnerships, there are doubles that mean still something else.
The most common doubles have fairly defined meanings and are easily recognized as to what kind of double they are when they occur. However there are some instances when it is less than clear what a double should mean in specific circumstances – instances when logic supports the usage of two different but both logical meanings for a double. In these cases, it’s partnership agreement or the lack of partnership agreement that should determine how such doubles should be interpreted.
Here is an instance of a double for which there are two possible logical meanings for the double.
The Bidding at our table:
The first possible meaning for this double is that it shows good clubs (usually five or more in length). Thereby inviting the lead of clubs against a spade contract and inviting possible competition in clubs if opener’s passed hand partner has a club fit and a few useful HCP. If opener had a 2-suiter, he could bid his second suit at the two level, cue-bid 2
if he had a big reopening takeout double of spades (or by partnership agreement it could be used to show a good hand with a long running club suit w/o a spade stopper) and if he had a big balanced hand, one that he had planned to jump to 2NT after a one-level bid by partner, he could wait and if they settle in 2, then double. An advantage of playing this double as suit-showing is that if responder is broke (he usually will be), the partnership is not as “forced” to re-enter the auction as responder can pass the double or a bid by LHO. Using the double as “penalties” or suit-showing seems instinctive as doubling an artificial bid is traditionally used to show that suit.
The second possible meaning for this double is that it is a takeout double of spades. If the 1 overcaller passes, your passed-hand partner could show a diamond or heart suit at the two level or he could also raise clubs with three or four-card support, as opener should have a five-card club suit for this double (typically 1-4-3-5, 1-3-4-5). If playing double as takeout, bidding a second suit instead might show a five-card suit, especially if that suit was hearts since partner has failed to make a negative double for hearts, as he would have if he had four or more of them and a few useful points. Playing a double for takeout would mean that “cue-bidding” 2 should probably be reserved to show a long running club suit w/o a spade stopper while passing 2
and then doubling after a retreat to 2 could be used to show a somewhat penalty oriented, big balanced hand as mentioned previously.
Both meanings for a double of 2 (or probably after any double of the RHO’s cue-bid of opener’s suit after an overcall by opener’s LHO) have their advantages. So a partnership should decide which meaning of such a double is better than the other, and agree to that interpretation.
However without previous discussion of what a double of a two-level cue bid by RHO of opener’s minor opener after LHO has made a 1-level overcall means, the double IMHO should be interpreted as suit-showing, not for takeout. Partnership discussion & agreement is needed to play it for takeout.