The word "Immo-bilien" does not exist, and "bilien" is not a standalone word. The term "Immobilien" is a compound word that means "real estate" or "immovable property," such as buildings or land.
The word "Immobilien" is derived from the Latin components "im-" (meaning "not") and "mobilis" (meaning "movable"). "Bilien" has no meaning on its own and only makes sense when combined with the prefix "Immo-.