The word "specialism" refers to a specific area of expertise, knowledge, or focus. It means that someone has specialized in a particular field or subject, becoming highly knowledgeable and skilled in that specific area. Full definition
First, you must choose carefully and second, you must recognize the specific area of specialism in order to avoid an errors and omissions claim. (remonline.com)
He has a high degree of specialism in various aspects of contentious and non-contentious regulatory and financial crime matters including sanctions, AML and Anti Bribery & Corruption. (mccarthydenning.com)
The Institution of Mechanical Engineers, for example, provides a broad range of courses aimed at ambitious employees, often with specialisms in particular fields. (jobs.telegraph.co.uk)