View through conversion occur when user just see the ad and convert later.

Google Ads Help Center

For example: You run a banner ad on display network. Your banner ads is shown on various websites of display network. The user go to any website from display network, and see your banner ad there for just 1 second. If that user comes to your website and convert within 30 days of seeing your banner ad, it will be counted as View-Through conversion.

Conditions of recording View-through conversion

1. Your ad must be shown at least 50% on screen
2. Your ad must be seen for at least 1 second
3. User who have seen your ad, converts within defined conversion window.
4. User NEVER interacted with your ads

NOTE: If user interacts with your banner ad and convert later within conversion window timeframe, “view-through conversion” WILL NOT BE recorded. It will be counted as conversion but not view-through conversion.

Your “View-through conversions” column tells you when customers see, but don’t interact with your ad, and then later complete a conversion on your site. This is different from the data in your other conversion columns, which record when customers interact with an ad and then complete a conversion on your site.

Source: Google

About Conversion window

A conversion window is the period of time after an ad interaction (such as an ad click or video view) during which a conversion, such as a purchase, is recorded in Google Ads.

You can edit or choose your conversion window through the following settings.

1. Sign into your Google Ads account.
2. In the upper right corner, click the tools icon , and under “Measurement,” click Conversions.
3. Find the conversion action you’d like to edit. Click its name in the “Name” column.
4. In the “Settings” section, click Edit settings.
5. Click on Click-through conversion window. Select how long it takes to track conversions after an ad interaction from the drop-down. You can set it anywhere from 1 to 30, 60, or 90 days for Search and Display campaigns depending on the conversion source. Note that windows of at least 7 days are recommended, because they provide a richer set of conversion data.
   • For view-through conversions, click View-through conversion window and select an option from the drop-down.
6. Click Done.

What counts as a view-through conversion in a TrueView for action campaign?