A double standard is an ethical rule applied more stringently to one party than to others. Such an application is generally viewed as hypocrisy, but is more often condemned in the abstract, if it is condemned at all, while being simultaneously excused in the particular. When accused of using a double standard, advocates of that particular line of thinking typically either deny such an application altogether or claim that there are special, over-riding concerns which justify such an approach.
A traditional example in many societies is adultery and other sexual behaviors if it is socially more acceptable for a husband than a wife to have a lover. Similarly a man who has sex with many different women may be considered a "stud", while a woman who has sex with many different men may be considered a "slut" or a "whore", "tease", "tramp", etc... As a more accepted example, children are generally forbidden from acts such as drinking and smoking while adults are permitted to perform such acts.
In the context of religion many argue that accusations of blasphemy are an especially common example of double standard in that the very concept of blasphemy relies on applying or seeking to apply different standards to the theology seeking protection than to other matters.
Specific political examples are harder to give, because almost no one, be they liberal or conservative, will admit to hypocrisy, although both sides are quick to point fingers at the "liberal media" or "conservative media" for giving a "pass" to one side of the political spectrum while virtually slandering the other.
Doublestandards also violate the principle of justice known as impartiality, which is based on the assumption that the same standards should be applied to all people, without regard to subjective bias or favoritism based on social class, rank, ethnicity, gender or other distinction.
Efforts to defend real or purported doublestandards usually take the form of denying that a doublestandard is being applied or attempting to give a good reason for the disparate treatment (in which case it is a doublestandard but it is a favorable or acceptable doublestandard).
Proponents of this doublestandard would say that it is justified by natural law (men naturally cannot help it but women can and are thus supposed to function as the "gatekeepers"), while opponents would say that such an assumption is sexist and based on outmoded views of sexuality.
The concept that America holds a "DoubleStandard" in favor of Israel has been ramped up in recent years and has reached a peak now during this latest confrontation with Iraq.
The "DoubleStandard" is that all must view favorably the self-styled claims of Islam while dismissing the Jewish claim to the Land of Israel which dates back 4000 years.
"DoubleStandards" applied against the Jews in the 30s and 40s that spawned the Holocaust have been delineated competently in many, many books.(4) It is merely necessary to note that the simple phrase "DoubleStandard" was the very foundation operative in causing and actuating the Holocaust.