Definition
Two-way sync (sometimes called bi-directional sync) is an integration pattern where changes in system A propagate to system B and changes in system B propagate back to system A. Contrast with one-way sync, where data flows in a single direction. Two-way sync is harder: you need conflict resolution (what happens if the same record is edited in both systems at once?), change detection on both sides, and idempotent application of updates.
Most form-to-Sheets integrations are one-way: submission creates a row, edits to the row do not come back to WordPress. Two-way sync is useful when your sheet is also a working surface - a sales rep updates the Status column in Sheets and expects that change to flow back to the WordPress submission record, to a CRM, or to a triggered email.
How SheetLinkWP relates to Two-Way Sync
The Two-Way Sync add-on for SheetLink Forms registers a REST endpoint on your site that your Sheet calls (via Apps Script) whenever a tracked row changes. Cell edits are packaged into a structured change event and posted to WordPress, where you can hook them with the sheetlinkwp_sheet_update action to trigger CRM updates, status change emails, or custom workflows. Conflict resolution uses last-write-wins on a per-column basis, with an edit timestamp column to adjudicate.