BigCommerce supports 'metafields', which contain additional data that can be stored at product and variant level. Some third party vendors may utilise metafields for storing information such as review data, analytics or any other values they require for a particular integration.
Klevu does not index these metafields by default. This is because they require additional API requests to be made during our data feed creation, which will ultimately slow down your store synchronisation with Klevu. If you need these metafields to be indexed, this can be enabled via the Klevu App Settings: