NSEs are non-consensual sexual experiences (e.g., sexual abuse, assault and rape). The term NSE is sometimes used in scientific literature as an umbrella term in order to describe a broad range of experiences.
A 'safeword' is a code word or phrase (or a series of code words/phrases), or even a physical gesture or signal that is used during sex to communicate a physical or emotional state.
In BDSM 'limits' are activities that people feel strongly about. Often strongly enough that they are prohibited. BDSM participants typically discuss and negotiate their limits with partners before any activity takes place. It’s essentially a more comprehensive consent conversation. There is a distinction made between hard and soft limits: