はさておき means 'setting aside' or 'leaving aside' and is used to temporarily put a topic out of consideration so you can talk about something else. It often implies that the set-aside topic is important but not the current focus. You attach it directly after a noun or noun phrase, as in 冗談はさておき (jokes aside). The phrase carries a nuance of 'we can discuss that later, but for now...' and is common in both speech and writing, though it sounds slightly formal. In casual conversation, you might hear はおいといて (a more colloquial variant), but はさておき is standard and safe for N1. It can also be used to politely steer a conversation away from an awkward or sensitive subject.