Myriad means a huge number of something, so many that you'd have trouble counting them all. When a meadow has myriad wildflowers, it's covered with thousands or even millions of them in every direction. When a scientist studies the myriad stars in the galaxy, she's looking at countless billions.

You can use it as a noun (“a myriad of possibilities”) or as an adjective (“myriad reasons”). Either way works well.

What makes myriad useful is that it captures abundance and variety at the same time. A library has myriad books on thousands of different topics. A coral reef has myriad species in every color and shape imaginable. The word suggests both quantity and overwhelming diversity.

When you face a complicated problem, you might need to consider myriad factors: dozens of different things that all matter. When you're excited about summer vacation, you might think about the myriad activities you could do. The word helps express that feeling of endless possibilities or overwhelming complexity.