related to; in relation to; concerning
Formal written expression used to introduce a topic or subject matter. Often appears in official documents, news, and academic writing. Synonymous with に関して (にかんして), but に関し is slightly more formal and concise.
Please share your opinion concerning this issue.
I have several questions regarding the new product.
につき can mean 'concerning' in formal notices much like に関し, but it also has a separate 'per' meaning that に関し lacks.
に関し introduces a topic ('concerning X'), while に対して marks a target of an action or attitude ('toward X'), so they are not interchangeable despite similar sentence position.
The continuative form of 関する, followed by the case particle に; に関し is the formal connective form underlying に関して.