There is a tradition which has been mentioned in Sahih al-Bukhari and other books of Hadith. The wording of the tradition is:
Copy Arabic text
(Sahih al-Bukhari, hadith no. 1903)
The translation of this hadith is: "If a person does not refrain from falsehood and from acting upon falsehood, then God does not require him to abstain from eating and drinking." It is well understood what is meant by lying. For example, if you are in Delhi right now but say that you are in London,  or, you offer namaz without ablutions, but claim that you took a bath and did ablutions before offering prayer, then these are examples of lying. 

Now the question is: What is the meaning of acting upon falsehood?
Today, when I read the news, I realized what it means to 'act upon falsehood'. An example of this is to claim to follow Islam, but to practically live in falsehood. 
The translation of the word 'zur' in the above hadith is falsehood. Falsehood is the best translation of the word 'zur'. Generally, people translate 'zur' as 'kizb', but according to me, the right meaning of 'zur' is expressed by the word 'falsehood', and not by 'kizb' or lying. 
The above hadith speaks about a person who abstains from food and drink during Ramadan, but continues to tell lies. Here, telling lies means to say something which is against reality.  Lying is a very comprehensive word. To say you are in London when you are actually in Delhi is not the only instance of lying.  There are a thousand forms of lying. To do patch-up, to twist your words, to manipulate, to express something from your lips while your heart feels something else -- are all forms of lying.  There is no limit to such lying. There are innumerable forms of lying. A person can himself understand whether or not he is lying. A person's conscience always guides him. If a person introspects, he will himself understand whether he is twisting his words, doing patch-up, or speaking the truth. 
A person must completely refrain from lying. He must refrain from every kind of lies. He must refrain from openly telling lies as well as from secretly speaking lies. Only then will he be regarded as a person who does not lie. 
Now the question is: What is the meaning of acting upon falsehood?

According to me, this is when a person gives an appearance that he is obeying Islam, but in reality he is only following his own desires.
These are occasions when a person is involved in his own politics, follows his desires, or engages in worldly activities, but gives the appearance of adhering to Islam.