This indicates an attack attempt against a Cross-Site Scripting vulnerability in Magento.
A user can insert script in the address field, which can potentially introduce a Denial-of-Service vulnerability.
Magento 2.0 prior to 2.0.18
Magento 2.1 prior to 2.1.12
Magento 2.2 prior to 2.2.3
Denial of Service
Apply the latest update from the vendor.