The phrase "small bathtub" refers to a small-sized tub used for bathing. It means that the bathtub is not very big and can hold less water compared to larger tubs. Full definition
If you are worried your bathtub is not pretty enough, these images prove that even if you have a small bathtub with no natural lighting, your images will be beautiful. (annicamariephotography.com)
There are a great option for smaller bathtubs or if you only have a shower stall because they take up less room. (earlymomentsmatter.org)