How to retrieve all nodes for a taxonomy term using Services?
I found out how to do it, so I am posting it here in case it is helpful to somebody.
Feel free to post if you know a better way.   

I assume you have created some content with fields corresponding to taxonomy vocabularies.    


Create a Services View    


Install the Services View module, as suggested in my previous comment.    
Go to Structure / Views / Add new view    
Give your view a name and uncheck 'create a page' because we just want a service.    
Click 'Continue &amp; Edit', you should then be in the 'Displays' screen.    
Click on the '+Add' displays button, select 'Services'.    
Under 'Service Settings' click on the path and change it. e.g my_view_path.    

Create criteria for your view    


Under 'Filter Criteria' click 'Add'. Do not use Advanced/Contextual Filters.    
Search for your field, and click Apply'    
'Autocomplete' in the Selection Type, 'Apply and Continue'. It should not matter because we are going to call this from a URL, not a web page.    
The 'Configure filter criterion' popover is shown.    
Check 'Expose this filter to visitors'. If you don't do this, you will not be able to pass as an argument.    
Scroll down to the bottom and click on 'More'.    
Take note of the 'filter identifier'. This is the name of the argument you need to pass in the URL, e.g: field_myterm_tid    
Click on Apply filter    
Repeat for other filter criteria as needed.    
Click on Save View    

Enable the Service Resource    


One last step, go to Structure > Services    
You should see a list of endpoints, click 'Edit resources'    
Check to enable the resource you just created.    

Finally, retrieve your info with HTTP GET    



    http: //myserver/my_endpoint_path/my_view_path?field_myterm_tid=XX&amp;field_myterm2_tid=YY



XX and YY are the textual names of the terms