Sterile fluid containing 0.9% sodium chloride solution commonly used for IV (intravenous) infusions.
Has an osmolality of about 280 which is roughly equal to the normal blood osmolality.
Also used for washing, irrigation (no, not for your house plants!) and maintaining pressure.
It costs about A$2 per 1 litre bag here in Australia.
To make your own saline, stir about 9g of table salt into one liter of water. To make your saline suitable for medical purposes, make sure your water is clean and sterile, that the salt you use is pure and that all instruments and containers used are sterile.
Non medically sterile homemade saline is nevertheless useful for such things as washing eyes out and cleaning wounds - it hurts less than tap water as the osmolality is close to that of plasma.