what is data cleaning? how is it done?

I can simply say it as Purifying the data.

Data Cleansing: the act of detecting and removing and/or correcting a databases dirty data (i.e., data that is incorrect, out-of-date, redundant, incomplete, or formatted incorrectly)

data clensing is nothing but standidizing and reformatting ( encoding,decoding,data type conversion) the data before we store the data in the warehouse.

it is a process of identifing and changing the inconsistencies and inaccuracies

It is nothing but purifying data , the extract process always exposes the data qulaity issues that have been bured within the operational source system. Since the data qulaity significantly impacts data warehouse credibility , you need to address these qulaity problems during the data staging which is nothing data cleaning.

Could you please give me one real time example How we do data cleansing.....