Here are 10 terms that may be heard frequently related to the Russian invasion of Ukraine.
The capital city of Ukraine, home to approximately 2.9 million people.
Article 5 of NATO's Washington Treaty states that if one of its members is attacked, it is considered an attack against all members and that there will be a "collective defence." The first time it was invoked was after the Sept. 11, 2001 attacks.
Ukraine is not a member of NATO.
Sanction or targeted sanction
It's an intervention meant to influence or coerce a person, organization or country toward a specific action or outcome. The most common sanctions being considered or implemented against Russia and its president, Vladimir Putin, are economic in nature.
Society for Worldwide Interbank Financial Telecommunications (SWIFT) is a Belgium-headquartered consortium used by banks and other financial institutions that serves as a key communications line for commerce worldwide. About half of all high-value payments that cross national borders go through its platform.
Ukraine has sought for Russia to be excluded from SWIFT, but several European leaders would prefer to stay patient because a ban could make international trade more difficult and hurt their economies.
Lethal aid and non-lethal aid
Lethal aid is a diplomatic term for deadly weapons. Non-lethal aid consists of non-military supplies such as medical or communications equipment.
As explained by Scott Radnitz, an associate professor for Russian and Eurasian Studies at the University of Washington, a false flag attack could include an attack by a government against its own forces. The aim is to make the world think the attack was perpetrated by a hostile force.
There were accusations before the invasion that Russia might use such a false flag to justify action against Ukraine.
Soviet Union, or USSR
The longtime superpower that was broken up in 1991 into several smaller nations, including Ukraine. Russia is the largest remaining piece of the former USSR.
Putin talks repeatedly about the humiliation of Russia after the Soviet collapse. There is a belief by some that his attack on Ukraine is part of a desire to re-establish the Soviet state or something similar.
Chernobyl is a decommissioned nuclear power plant and scene of the world's worst nuclear disaster. When it was still within the Soviet Union, the reactor exploded in April 1986, spewing radioactivity across Europe. The exploded reactor has been covered by a protective shelter to prevent radiation leak.
Russian forces reportedly gained control of Chernobyl on the first day of the invasion.
A region in eastern Ukraine where Ukrainian forces and Russian-backed separatists have been at war since 2014, killing 14,000 people.
An area which Russia annexed from Ukraine in 2014.
The Associated Press contributed to this report.