Tex. Educ. Code § 37.0021. Use of Confinement, Restraint, Seclusion, and Time-Out.

...

(b)  In this section:      

                                                  
    (1)  "Restraint" means the use of physical force or a mechanical device to significantly restrict the free movement of all or a portion of a student's body.

    (2)  "Seclusion" means a behavior management technique
in which a student is confined in a locked box, locked closet, or locked room that:
(A)  is designed solely to seclude a person; and                            
(B)  contains less than 50 square feet of space.