Multi-tiered Systems of Support is a best practice framework that encompasses supports for the whole child, and takes into account academics, behavior, and social/emotional supports. MTSS is an umbrella term use to describe practices in your school, including, RtI and PBIS, however it is not limited to these two supports. The Texas Education Agency provides an excellent Q&A here that helps to describe what MTSS is and isn't. 

Trauma-Informed Care is an approach, based on knowledge of the impact of trauma, aimed at ensuring environment and services are welcoming and engaging for students and staff. Studies now show that nearly every school has children who have been exposed to overwhelming experiences, such as witnessing violence between their caretakers, being the direct targets of abuse, and other kinds of adversity that considerably impacts learning.