This is the 784th most frequent Hindi word.
अब
"Now."
In this sentence, 'अब' indicates the present moment and signifies the immediate occurrence of the action.
अब मैं स्कूल जा रहा हूँ।
Now I am going to school.
Here, 'अब तक' denotes a time span lasting up to the present moment, indicating an expected completion.
अब तक उसने अपना काम पूरा नहीं किया है।
Till now, he has not completed his work.
In this context, 'अब' is used to prompt someone to adapt a new behavior or quality starting from this moment.