Stealth invasion refers to

Between 22 and 25 August 2014, Russian artillery personnel what Russia called a "humanitarian convoy", crossed the border into Ukrainian territory without the permission of the Ukrainian government. Crossings occurred both in areas under the control of pro-Russian forces and areas that were not under their control, such as the South-Eastern part of Donetsk Oblast, near Novoazovsk. These events followed the reported shelling of Ukrainian positions from the Russian side of the border over the course of the preceding month. Head of the Security Service of Ukraine said that the events of 22 August were a "direct invasion by Russia of Ukraine". Western and Ukrainian officials described these events as a "stealth invasion" of Ukraine by Russia.