Line of Credit is essentially a facility to allow access to the equity that has been built up in your home (or investment property).
It can be considered like a large overdraft (or credit card) where a "credit limit" is established, and money can be paid in, and withdrawn again up to the original limit at any time. The line of credit is far cheaper than most credit cards due to attracting interest rates that are similar to home loan rates.
A line of credit can generally be used for any purpose, although many lenders do have restrictions on specific purposes.
Line of credit is generally not recommended to be used as a home loan, as it can be difficult to determine exactly how much you have repaid, and how much you have spent, from month to month. As a home loan, a safer option can be a standard variable loan with redraw or offset.