All these terms hypothecation, lien, charge, pledge and mortgage have the same meaning. The most common use of these terms would be when someone takes a secured loan i.e. a loan which is secured by a collateral such as applying for Bajaj Finserv Loan Against Property.
If we talk about the definition,
Mortgage refers to an agreement between a borrower and a lender wherein a borrower secures a certain amount as funding against their real-estate property. This is one reason loans such as loan against property wherein the mortgaged asset is mostly a residential flat or a building or a piece of land qualifies as a mortgage loan.
Hypothecation, on the other hand, is the practice where a debtor pledges collateral to secure a debt or as a condition precedent to the debt, or a third party pledges collateral for the debtor. If you observe properly, the definition is very similar to the definition of mortgage.
Moving on to lien, it refers to a condition put forward by the borrower which basically makes the transfer of property possession temporary. As per the definition, lien means a right to keep possession of property belonging to another person until a debt owed by that person is discharged.