"back then" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "prepositional phrase",
        "head": ""
      },
      "expansion": "back then",
      "name": "head"
    },
    {
      "args": {},
      "expansion": "back then",
      "name": "en-PP"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "prep_phrase",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Time",
          "orig": "en:Time",
          "parents": [
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2022 January 12, Nigel Harris, “Comment: Unhappy start to 2022”, in RAIL, number 948, page 3",
          "text": "On the East and West Coast Main Lines in the 1950s/60s, for example, we saw the extinction of intermediate stations in order to create the same sort of accelerations that IRP is now promising. Back then, the priority was faster main line services, with wayside/intermediate stations paying the ultimate price.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "At that time, at the time referred to in the past."
      ],
      "id": "en-back_then-en-prep_phrase-RZskYY9q",
      "links": [
        [
          "At that time",
          "at that time"
        ]
      ],
      "related": [
        {
          "word": "back in the day"
        }
      ]
    }
  ],
  "word": "back then"
}

{
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "prepositional phrase",
        "head": ""
      },
      "expansion": "back then",
      "name": "head"
    },
    {
      "args": {},
      "expansion": "back then",
      "name": "en-PP"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "prep_phrase",
  "related": [
    {
      "word": "back in the day"
    }
  ],
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English prepositional phrases",
        "English terms with quotations",
        "en:Time"
      ],
      "examples": [
        {
          "ref": "2022 January 12, Nigel Harris, “Comment: Unhappy start to 2022”, in RAIL, number 948, page 3",
          "text": "On the East and West Coast Main Lines in the 1950s/60s, for example, we saw the extinction of intermediate stations in order to create the same sort of accelerations that IRP is now promising. Back then, the priority was faster main line services, with wayside/intermediate stations paying the ultimate price.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "At that time, at the time referred to in the past."
      ],
      "links": [
        [
          "At that time",
          "at that time"
        ]
      ]
    }
  ],
  "word": "back then"
}