1) Lasting for many years 2) Lasting quite a while 3) Like some mortgages 4) Like some relationships 5) Not transient 6) Type of lease or loan 
Three or more years. In the context of accounting, more than 1 year.
In accounting information, one year or greater. 
In accounting terms, one year or longer.
The expressions 'short term', 'medium term' and 'long term' mean different things in different... <a target=_blank href='http://www.finance-glossary.com/terms/long-term.htm?id=1580&ginPtrCode=00000&PopupMode=false' title='Read full definition of long term'>more</a>
The expressions short-term, medium-term and long-term mean different things in different contexts... <a target=_blank href='http://www.finance-glossary.com/terms/long-term.htm?id=12839&ginPtrCode=00000&PopupMode=false' title='Read full definition of long-term'>more</a>
memory that we hold on to for a long time
covering a relatively long period of time: a long-term lease. · maturing over or after a relatively long period of time: a long-term loan; a long-term bond. · (of a capital gain or loss) derived from the sale or exchange of an asset held for more than a specified time, as six months or one year.