I see a lot of artist websites where they’ve gone throught the trouble of dividing their images into small manageable portfolios but then they’ve named them things like "portfolio 1", "portfolio2", etc. What a wasted opportunity!
Your portfolio names should draw visitors in and entice them to have a closer look. At the very least, portfolio names should accurately describe the group of images contained within the portfolio.
Look at the grouping and decide what this set of images have in common. After all you grouped these images together for a reason. Was it by subject matter? Medium? The feeling they gave you at the time? Whatever the reason, capitalize on that and give each portfolio a meaningful title.
It could be very basic: Landscapes, Portraits, Still-lifes. Or, it could be more complex, related to specific themes: such as equestrian art, americana, fantasy art, etc.
There is an added bonus to doing this. Usually these titles are marked in such a way that they tell search engines that this title is considered important. Making these titles specific and descriptive is much better for your search engine results than "portfolio 1", etc.