In classical music what does op 10 No 1 mean?

Op 10 No 1 stands for "Opus 10 Number 1". It is a numbering system used to identify compositions by classical music composers. The term "opus" (abbreviated as "Op") is used to refer to a composer's body of work, and is typically given to a collection of pieces that are related to each other in some way, such as being grouped together by genre, style, or instrumentation. The number following "Op" indicates the order in which the composition was published, with "No 1" signifying that it is the first composition within that opus. For example, Op 10 No 1 would refer to the first piece in a composer's tenth published collection.