  Temporal sentence grounding in videos (TSGV), \aka natural language video
localization (NLVL) or video moment retrieval (VMR), aims to retrieve a
temporal moment that semantically corresponds to a language query from an
untrimmed video. Connecting computer vision and natural language, TSGV has
drawn significant attention from researchers in both communities. This survey
attempts to provide a summary of fundamental concepts in TSGV and current
research status, as well as future research directions. As the background, we
present a common structure of functional components in TSGV, in a tutorial
style: from feature extraction from raw video and language query, to answer
prediction of the target moment. Then we review the techniques for multimodal
understanding and interaction, which is the key focus of TSGV for effective
alignment between the two modalities. We construct a taxonomy of TSGV
techniques and elaborate the methods in different categories with their
strengths and weaknesses. Lastly, we discuss issues with the current TSGV
research and share our insights about promising research directions.
