It is a word many of us heard a lot of in the run-up to the EU referendum and in the nine months that followed following the result.
The Prime Minister is expected to formally invoke the Article 50 Bill by the end of the month and formal negotiations with countries in Europe and further afield will begin.
As politicians argue over the details of how Britain will withdraw its membership of the European Union in the coming weeks and months, ITV Wales has been meeting families in both Wales and abroad who fear their futures are at stake.
Because freedom of movement laws, Brits and Europeans are able to live, work and travel freely within the EU.
Wales This Week travelled to the Costa Blanca to hear concerns of Welsh expats living in Spain, and those from Europe who have chosen to call Wales their home.
One in three Brits living in Spain are retired.
But a life filled with sun, sand and sangria has been overshadowed since Brexit.
The small Spanish village of Torremendo, near Torrevieja, is home to expats Stuart and Aline Burnley.
Aline and Stuart ran a milk delivery service in Tenby and sold everything 13 years ago to make the move.
But a falling exchange rate and low property prices are effectively trapping them in Spain, and they told ITV Wales the added uncertainty of Brexit worries them.
Part of the Brexit negotiations is healthcare, and there is currently no guarantee UK citizens living abroad will have access to the free European system.
Aline suffers with a number of health conditions include Type 2 Diabetes and relies heavily on the free service in Spain.
One private healthcare quote she received was over 24,000 euros a year.
Wales is home to a variety of cultures, religions and races.
And since Britain joined the EU in 1973, many European citizens took the opportunity to work, live and travel here.
That is what Justyna Tull from Poland did in 2008.
She met her husband Stephen while on holiday in north Wales and after a few years of a long-distance relationship, she made the permanent move to Wales.
They are now married and have two sons together. She works for a laboratory for the NHS that does genetics work and he is a teacher.
But, they are both fearful over what Brexit could mean for them - particularly in terms of residency and employment.
See more of their stories on Wales This Week tonight at 8pm on ITV Cymru Wales.