Like the majority of Microsoft Desktop Applications, both Project and Visio are licensed on a PER DEVICE basis.
That means that any device which is used to access the software in any way requires an appropriate licence (in your case Project and Visio) to be assigned to it. It does not matter whether the software is deployed locally on the Device or whether the device will access the software via a server such as a Terminal Server ... any device which accesses the software in any way will require a licence!
It also does not matter how often your users are intending to use the software. Whether they use it 5 minutes a day, 5 minutes a week or 5 minutes a month, they still require a licence to be assigned to them.
Please note some additional points which are very relevant:
If we are talking Versions 2007 or 2010 of Project and Visio and you intend to provide access from a server (instead of the software being locally deployed on the client device) then the licenses you acquire and assign to the relevant devices must be acquired through a Microsoft Volume Licence Agreement. Full Packaged Product (FPP) and Original Equipment Manufacturer (OEM) licenses for Version 2007 or 2010 do not contain licence terms which would permit access to the software deployed on a server!
Another note ... although you have 10 users, ... as I have said above, Project and Visio are licensed per device ... so if it works for you to have a single device with Project and Visio deployed on it which is shared by those 10 users when they need it .. then you could reduce the amount of licenses you require to one Project and one Visio ... as there is only one device which has the software installed on it.
Another rule to keep in mind ... once a Microsoft Desktop Application licence (such as Project and Visio) is assigned to a device ... it can not be re-assigned to another device for a period of at least 90-days. So dont make the mistake that others have in the past ... where they thought they could buy one licence ... let a particular device use it for a few hours or days .. and then reassign the licence to another device so that the new device could then use the software or access the software for a few hours or days for example. The 90-day rule strictly prohibits transferring those licenses inside a 90-day timeframe.
As a former licensing auditor I have seen many organisations make this mistake! It can be costly!