A triple band metamaterial absorber in the terahertz range, incorporating a three closed circle ring resonator, was designed and fabricated on flexible polyethylene terephthalate "PET" substrate. The proposed design was investigated theoretically and experimentally. Computer simulation technology "CST" was used to study the designed structure, while lithography technique was used to fabricate the absorber and terahertz time-domain spectroscopy was utilized to measure the reflectivity. Results showed the presence of three intensive peaks at the resonance frequencies of '0.43, 0.61, and 0.88 THz', which correspond to the absorptivity of 98%, 91%, and 98%, respectively. The sensitivity of the three peaks was found to be '70.5, 133, and 149.5 GHz/RIU', respectively. The parametric studies and field distributions were analysed. Furthermore, the proposed design exhibited polarization insensitivity for both transverse electric "TE" and transverse magnetic "TM" modes from 00 to 900. It was concluded that the proposed design can be specifically viable for some important applications such as 'THz' images, filtering, biological sensing, and optical communications.