Rapeseed oil is a specific oil, just like soya bean oil, olive oil & sunflower oil. All these oils have very different culinary uses but are all vegetable oils.
Vegetable oil is a generic term covering all oils produced from plants including edible cooking oil as well as non edible oil for healthcare or technical use.
It is presumed when buying vegetable oil from a cash and carry or a supermarket that the oil is an edible oil suitable for cooking.
If you find an oil labelled as vegetable oil, you will need to look at the ingredients on the bottle or tin to find out which oil has been packed. Usually when buying vegetable oil you will find the oil being packed is the cheapest on the market, as the vegetable oil market is price driven. Historically this has been refined soya bean oil, which now comes from GM plants. Supermarkets are becoming more aware about oils from GM sources and so sometimes when buying vegetable oil from supermarkets, they have bottled rapeseed oil.Supermarkets may not have labelled the oil specifically as rapeseed oil as opposed to vegetable oil as many people (including chefs) still refer to general purpose edible oil as vegetable oil. Usually when supermarkets bottle rapeseed oil under the generic term vegetable oil, there is a picture or illustration of rapeseed flowers or plants on the label. It is important to know which oil you are using as although both soya bean oil and rapeseed oil are refined and can both be used for the same purposes each has their pros and cons of each use.
Rapeseed oil has lower omega 6 and comparable omega 3 to soya bean oil, therefore is healthier when larger quantities of oil are consumed, such as when frying absorbent food or used in mayonnaise, sauces and dressings.
Soya bean oil has a more consistent colour, whereas rapeseed oil can change between pale yellow, to having a greenish tinge.To summarise, rapeseed oil is a vegetable oil but vegetable oil is not necessarily rapeseed oil. Not all vegetable oils are edible cooking oils, but the term vegetable oil is commonly accepted as an all purpose edible cooking oil.