It basically means the total income that you are entitled to receive from the rental or exploitation of real property(hence the use of the word "δικαιωμάτων" which means "rights" or "royalties").

See:

Every year the value of 1/3 of the total rental rights, is determined by an independent valuation expert and if needed impairment is recognised. Based on the ...
http://www.vbk.nl/media/870763/bijlage_1e_draft_jaarrekening...


Report income on line 21 and expenses on line 36 of Form 1040 (PDF), U.S. ... Examples of expenses that you may deduct from your total rental income include:
https://www.irs.gov/taxtopics/tc414.html

I'm working my way through the US tax maze and had a question. ... be clear, it is 2 apartment I would be letting out; total rental income of £90k,
http://britishexpats.com/forum/usa-57/tax-uk-rental-income-7...
...

and

If the total property income is less than £15,000 a single type 0 expense may be entered for the total expenses. The following cannot be claimed: trustee's or ...
http://help.iris.co.uk/IRIS/ODL/Product_Help/Trust_Tax/Edit_...

6 Apr 2014 - If your total property income (including FHL income) before expenses is below £81,000, add up your FHL expenses and put the total in box 9.
https://www.gov.uk/government/uploads/system/uploads/attachm...