What are 'boiling potatoes'?

This most likely means waxy potatoes, typically white or red. In some contexts it might also mean you want small ones so that you can boil and serve them whole, but it doesn't look like that's the case here.

There are two main kinds of potatoes, starchy and waxy. Starchy ones (like russets) cook up fluffy and dry, desirable for things like baked potatoes and fluffy mashed potatoes, but are prone to disintegrating when boiled or mixed into potato salad, and can get waterlogged from over-boiling. Waxy ones (like most red and white potatoes) on the other hand stay relatively firm, making them good for boiling.

So "boiling potatoes" meaning "potatoes for boiling" would indicate waxy potatoes, and that's consistent with the recipes you linked to. For aloo gobi, you want firm ones so they don't fall apart when you mix it all up. For curries and stews, you don't want them to get waterlogged or fall apart. Fries are much easier to handle if they're not falling apart! And two of the recipes even mentioned red and white potatoes.