Hello student,

This term "haplo diplontic life cycle" Related to plant life cycles.  in plant life cycle in sporic meosis The zygote divides to produce a deployed sporophyte. The sporophyte creates spores via same process and then those divided & produces haploid called gametophyte via mitosis. Gametophyte now make gametes via Mitosis. in some fungi this gametophytes are ofsmall size and short lived ,so those called haplo-diplontic life cycle.

Hello,

Haplo-Diplontic Life Cycle :

This kind of life cycle is seen in bryophytes and pteridophytes . In bryophytes a independent,dominant,photosynthetic, thalloid or erect phase is represented by a haploi gametophyte and it alternates with short lived multicellular sporophyte totally or partially dependent on the gametophyte for its nutrition. In pteridophytes the diploid sporophyte is dominant, independent, photosynthetic, and vascular plant body.It alternates with a multicellular, saprophytic , independent and short lived  haploid gametophyte. Ectocarpus , Polysiphonia  and kelps are haplodiplontic .