General Obligation bonds are secured by "taxes" primarily, whereas revenue bonds are secured by the "income" from the issuer of that particular bond.

"Secured" is a term applied to when a person signs personally for a lease.

it is lease paid on capital invested

Is called a lease.

Lease obligation is like debt in that both legally obligate the firm to make a series of specified payments. bondholders would like the firm to limit its lease obligation for the same reason that bondholders desire limit on debt: to keep the firm's financia burden at manageable levels and to make the already existing debt safer.