What does it mean that Jesus Christ conquered death?

from the old testament

• The fall of mankind in the garden of Eden brought with it a curse that includes death for all those who sin (Genesis 2:17). Jesus, however, did not sin. Instead, He died, perfectly God and man and perfectly innocent and sinless so He could conquer sin and death just as promised (Genesis 3:15).
• The key to Christ conquering death lies in the word "forevermore." Other people have died and been resurrected, but they all ended up dying again (1 Kings 17:17-24; 2 Kings 4:32-37). Only Jesus was resurrected, never to die again.
• Not only was Jesus's death and resurrection a fulfillment of His own words, it was a fulfillment of numerous Old Testament prophecies about the Messiah (Psalm 16:10; Isaiah 25:8; Hosea 13:14).

from the new testament

• Jesus Christ triumphed over death through His resurrection. He died and rose again on the third day, never to die again—and this is how He truly conquered death. Jesus said, "I am the first and the last, and the living one. I died, and behold I am alive forevermore, and I have the keys of Death and Hades" (Revelation 1:17-18).
• Jesus is the only religious leader who predicted His own death and subsequent resurrection (Matthew 16:21), taught based on that (John 2:18 -22; Matthew 27:40, 62-66), and made good on His word (Luke 24:6; 1 Corinthians 15:3-7).
• Jesus ascended into heaven where He remains seated at the right hand of God (Acts 1:6-11; Luke 22:69; Romans 8:34).
• Jesus was able to conquer death because He is sinless. Peter says, "It was impossible for death to keep its hold on him" (Acts 2:24, NIV).
• Romans 6:23 says, "The wages of sin is death" yet Jesus lived without sin (1 Peter 2:22); therefore, death could have no power over Him. The rest of Romans 6:23, contains the good news: "For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord."
• Jesus gave His life voluntarily so that we might, in Him, be saved from the eternal curse of sin (John 10:17).

implications for today

Before His death and resurrection, Jesus spoke of what was to come—eternal life: "I am the resurrection and the life. Whoever believes in me will live, even though they die. Everyone who lives and believes in me will never die" (John 11:25-26, CEB; cf. John 3:16; Acts 16:31). As believers in Christ, we no longer have a fear of death because, in Christ, we have the promise of eternal resurrection. Jesus said, "Because I live, you also will live" (John 14:19). Christ alone conquered death, and now we, too, can be "more than conquerors through him who loved us" (Romans 8:37).

Everyone who puts their faith in Jesus, trusting in His death and resurrection for the forgiveness of sins can be saved. The second death has no bearing on them, and after we die in this world, we have assurance that we will be in His presence for all eternity. Praise Jesus, for He alone conquered sin and death.