Different types of greases are typically formulated with three grease components: Base Oil, Thickener and Additives.
The base oil lubricates, reducing friction between moving surfaces; this is exactly the same role that the base oil plays in a lubricant oil
The thickener acts like a sponge; its job is to hold oil in reserve until needed to lubricate. The thickener responds to external forces such as movement, vibration or temperature as a trigger to release oil.
The additives supplement the lubricating capability of the base oil, improving upon characteristics such as wear protection and rust prevention.
I'm frequently asked if synthetic oil-based greases are really better than mineral oil-based greases.