Concentrates generally contain a higher % of THC than hash products. The common theme of all concentrates is they use some type of solvent to extract the THC. In the later part of the process, the solvents and plant matter are removed from the concentrate.
The 2 most common types of solvents used in the extraction process are butane or CO2. One criticism of concentrates is that it’s unlikely for all the solvents to be fully removed from the product. This is why CO2 extraction has become more popular than butane extraction. CO2 is harmless while consuming butane spells bad news. With that said, professional concentrate manufacturers have become extremely efficient in removing butane, so don’t write off butane extracted concentrates too quickly.
Oil is what is usually used in vape pens, such as the open vape. BHO, or butane honey oil, is very common in Colorado. Recently CO2 honey oil has gained popularity, as it poses no issues for lingering solvents in the concentrates. Oil is sticky like honey, and will string if you dab it.