Of course they come in various sizes, so it means anything from 1.5 m³ to just over 6 m³. A very rough measure, in other words, which makes sense in context.
("Container" is both "container" and "dumpster" in Swedish, and it's pronounced pretty much as "container" in English since it's a loan word, but the meanings have diverged, I guess.)
Anyone would like to give me the definition in SI?