If you browse many of the larger online sex shop retailers you'll usually find a product category called lesbian sex toys. Whether retailers have created this category in response to customer requests or because they want to appeal to as many demographics as possible, it's worth taking a moment to think about what it means for a sex toy to be good for lesbians, and if someone who identifies as a lesbian would necessarily want a sex toy that is supposed to be for lesbians.
The first thing to know is that sex toys are not made for a kind of person, or a particular identity. Sex toys are more like tools. How they function and who they work for depends largely on who is wielding them, and why. Also, sexual orientation does not determine what someone wants to do sexually. People who identify as lesbians have all kinds of different sex. It's not as if there's a club and you can only join if you follow certain rules.
If you want a sex toy in order to feel pleasure in or on your body, then there's no guarantee that a broad category like "lesbian" is going to deliver what you want for your body (which after all is completely unique, regardless of your sexual orientation). On the other hand, if you want a sex toy that will make you feel more like a lesbian (whatever that means) then it's possible that buying a sex toy with the word lesbian on it will be what you want.
Practically speaking, lesbian sex toys usually refer to toys that are designed to be used by two people with women's bodies. This might seem straightforward, but it isn't always. All women (despite what the anatomy books tell us) do not have the same bodies, the same body parts, and do not feel pleasure in the same places. There may be some generalizations that you can make, but when you are having sex with someone you need to learn about their body, not rely on what you've learned about all bodies called female.
If you're still curious what constitutes a lesbian sex toy just do a web search, or visit your favorite online sex shop. Usually retailers put products like strap ons and double dildos in these sections, and then the fill it out with other products which may or may not make any sense for someone who identifies as lesbian.
One last point worth making is that lesbian sex toys almost always refer to toys for two people to use. Of course plenty of lesbians are single and yet they are still lesbians, even when they are shopping for sex toys for themselves.