1. What does it mean?
스펙 comes from specification. Besides a product's technical specs, Korean uses it for a person's listed qualifications, such as education, experience, certificates, or test results. 스펙을 쌓다 means building that profile.
Also written or said as seupek
2. The nuance
It often concerns what can be presented on an application, not every aspect of someone's ability or worth. The English word specs is not normally used this way about job candidates.
3. Examples
“스펙 목록보다 프로젝트에서 한 일을 구체적으로 적었어.”
I wrote specifically about my project work rather than just listing credentials.
“지원 조건에 필요한 스펙부터 확인해 봤어.”
I first checked which qualifications the application required.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.