Blanco refers to Tequila that is unaged. They are also known as Plata or Silver. Typically Blanco’s are bottled shortly after distillation, although it is quite common for the spirit to be kept in stainless steel tanks for a few weeks before bottling.
The rules do allow for it to be in contact with wood for up to 60 days and still be called Blanco, although, the majority of distillers will call it a Joven Tequila (which is a Blanco that is either blended with a little bit of aged tequila or that has been aged for just a few weeks before bottling).