Parenchyma is functional tissue, i. e. tissue that has a specific function. Organs are built from functional tissue and connective/structural tissue (stroma). In the kidney this is e. g. Gerota's fascia (stroma) vs. the tissue producing urine (glomerula etc.).
You can look up more combinations of what parts of organs are parenchyma and which are stroma at e. g. Wikipedia: https://en.m.wikipedia.org/wiki/Parenchyma
The NIH definition reads: "Solid organ which consists of parenchyma and connective tissue stroma; the stroma subdivides the parenchyma into lobes, segments, lobules, acini, or cortex and medulla. Examples: lung, liver, spleen, kidney, parathyroid gland." (https://www.semanticscholar.org/topic/Parenchymatous-organ/1409347)
So in short parenchymatous organs are those that have parenchyma and are solid versus those that have a lumen or pouch or similar.