Placement refers to the sensation of where the sound "lives" in the mouth, which can commonly lead to a mouth posture that helps with an accent.
This is part 3 of 6 videos that offer you an introduction to learning accents.
Part 1: Accent vs Dialect vs Idiolect
Part 2: Phonetics
Part 3: Placement
Part 4: Intonation
Part 5: Helpful Hints
Part 6: Prioritizing Learning Accents