If you're a spouse, de facto partner, or dependent child included on someone else's Australian visa application, you'll see both "secondary applicant" and "subsequent entrant" used to describe your situation — sometimes on the same Department of Home Affairs page. They're related but not interchangeable, and which one applies to you changes what you need to prepare and when.
Secondary applicant: included in the same application
A secondary applicant is a member of the family unit — spouse, de facto partner, or dependent child — who is included in the primary applicant's visa application at the same time, in the same lodgement. Your documents (identity, relationship or dependency evidence, health, character) are submitted alongside the primary applicant's, and the application is assessed together.
Subsequent entrant: applying after the primary visa is already granted
A subsequent entrant is a family member who is added to a visa application after the primary visa has already been granted — for example, a partner or child who wasn't included at the time of the original application, or who becomes part of the family unit later (through marriage or birth). Subsequent entrant applications are lodged separately from the original, and don't require re-submitting the primary applicant's own evidence (skills assessment, employer sponsorship, points test documents, and so on) — only your own identity, relationship/dependency, health, and character documents, plus proof of the primary applicant's visa grant.
If you're not sure which applies to you: if the primary applicant already has a visa grant notice and you're applying separately afterwards, you're a subsequent entrant. If you're preparing your documents at the same time as the primary applicant, before any visa has been granted, you're a secondary applicant.
What ImmiAccount calls it
ImmiAccount and Department of Home Affairs correspondence generally use "member of the family unit" as the umbrella term for both, and the specific application type you lodge (combined vs. subsequent entrant) determines which form and process applies. [VERIFY: confirm current ImmiAccount terminology and exact form/process names, since Home Affairs occasionally updates portal wording.]
Why it matters for your document checklist
The practical difference is scope: a subsequent entrant checklist never includes the primary applicant's occupation, sponsorship, or points-test evidence — only your own documents plus proof linking you to the primary applicant's already-granted visa (their passport, visa grant notice, and Transaction Reference Number). VisaPacks has a separate, purpose-built checklist for each subsequent entrant visa type, listed below, so you're not working from a generic template that includes documents that don't apply to you.
Read the Subsequent Entrant Visas Explained guide for a walkthrough of what's actually required across all these visa types, including timing and evidence themes.