“Ekasana Pachhkan” (also written Ekasana / Ekashan Pachchakkhan) is a short phrase with two parts:

• Eka = one
• āsana (asana) = sitting / seat (here, one sitting for a meal)

So “Ekasana” = “one sitting” – in Jain practice it means one meal in one sitting in a day, during daylight.

• Pachhkan (Pachkhan / Pachchakkhan) = formal vow / resolve / pratyākhyān taken in front of Dev–Guru–Dharma (or mentally), to observe a certain restraint.

So, word by word:

• Ekasana = “one (eka) sitting/meal (āsana)”
• Pachhkan = “vow / formal resolve (pratyākhyān)”

Together: “Ekasana Pachhkan” = the vow to take only one meal in one sitting in a day.

You can see more explanation of Ekasana and its pachkhan here and specific Ekasana Pachkhan text here