Reducing friction or barriers to performing a behavior is simply making it easier or removing things that may be preventing someone from doing something.
This is a foundational technique in changing behavior, and part of the UK Behavioural Insights Team's 4-point approach ("Make it easy"). That said, knowing where the friction and barriers exist may not always be straightforward, and different groups of people may experience different barriers in different contexts.
Note: It is possible to remove too much friction. In a well-popularized study, a travel booking site found that delays in loading the best deals or travel options actually increased conversions. Similarly, longer input forms in digital interactions sometimes outperform, as people may consider the results more personalized or experience greater cognitive dissonance after having invested so much time in exploring the service.