custom_label
A custom_label is an optional tag you attach to products to group them however you want for campaign organization and bidding, with values you define yourself.
Channels like Google give you several custom label slots (custom_label_0 through custom_label_4). They have no meaning to the channel itself; they exist purely so you can slice your catalog the way your advertising strategy needs. Common uses include marking bestsellers, seasonal items, margin tiers, clearance, or price buckets.
They matter because they turn a flat catalog into something you can manage strategically. With a custom label like 'high_margin' or 'winter', you can build campaigns or set bids around the subset of products you actually care about, instead of treating every SKU the same.
In the feed, each custom_label field holds a short value you pick, and products with the same value can be filtered together in the ad platform. The main pitfall is inconsistency: misspelled or free-typed values fragment your groups and make them hard to target.
Because custom labels are usually computed from other data (margin, stock age, sale status), MartechFlow's rule engine is a natural fit. You can generate them from feed values, for example tagging anything where sale_price is set as 'on_sale', so the labels stay accurate on every refresh.