What is an ordinance in India?

Normally, a law in India is made only after all the parts of the legislature have had a chance to go through it and discuss it.

This is how laws are made in India:
https://tcpofindia.blogspot.com/2019/11/what-is-bill-and-when-does-it-become-law.html

But sometimes, the government needs to urgently make a law to take care of some situation, and both houses of the Parliament are not in session (are not working).
At such times, the Union Cabinet of ministers gets together, creates the law, and sends it directly to the President for Approval. The President can approve it and then it becomes a law for the time being.

Just like a law is PASSED, an ordinance is PROMULGATED.

Here are the important things about an ordinance: 

• It can be passed by the President of India only when at least one of the houses of the parliament (Lok Sabha or Rajya Sabha) is not in session. 
• It is passed under Article 123 of the Indian constitution. 
• The government must get it passed by the parliament within 7 weeks (42 days) of the parliament coming to work (convening). Otherwise, it lapses (stops being a law) 
• The governor of a state can also promulgate an ordinance for a state under Article 213 of the Constitution.