A wood stain is anything that changes the colour and appearance of wood. Although there are dedicated wood stain products, there are also many wood oils, waxes, varnishes and preservatives that both treat and colour interior and exterior wood.
The type of wood stain largely depends on the type of project and the type of finish required. For example, there are a huge range of stain colours, many that are 'wood tone' colours and others that are the primary colours. Wood stains are divided into those that require a top coat of varnish, oil or wax to seal in the colour, and those that are an all-in-one stain and sealer such as coloured waxes, varnishes and oils.
In the context of pure wood stains and dyes, wood dyes are simply more concentrated than stains allowing them to be thinned if required or intermixed with compatible products to colour and tint them.
Water-based stains are safe, low odour and very easy to apply. As they have very little smell, they're ideal for use on internal projects in confined spaces, such as for finishing wooden furniture and home crafts.
Solvent-based wood stains are very quick drying, usually just 5 to 10 minutes. Unlike water-based stains that may raise the grain of the wood slightly, solvent-based stains do not, meaning a smoother surface and finish can be achieved. Solvent-based stains are also more compatible with high moisture environment such as kitchens and bathrooms.
There are two types of wood stain. Most solvent or water-based stains just colour the wood. These stains need to be sealed in with a varnish, wax or oil. However, some products marketed as wood stains are all-in-one products that colour and protect / seal the wood. In the case of these products, there is no need to overcoat them with another product. If in doubt, always check the details on the back of the tin carefully before purchasing.