Keyword Analysis & Research: what do square brackets mean in javascript

Keyword Analysis

Keyword	CPC	PCC	Volume	Score	Length of keyword
what do square brackets mean in javascript	0.21	0.6	4452	26	42
what	0.52	0.1	7792	18	4
do	0.25	0.7	7336	45	2
square	0.53	1	8486	25	6
brackets	0.74	0.6	7579	88	8
mean	0.7	0.1	8999	91	4
in	0.12	0.8	3176	11	2
javascript	1.58	0.7	4356	29	10

Keyword	CPC	PCC	Volume	Score
what do square brackets mean in javascript	1.72	0.6	2012	76